Initial public release

20 files changed, 2748 insertions, 0 deletions

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
new file mode 100644
index 0000000..4b0e23f
--- /dev/null
+++ b/.github/workflows/build.yml
@@ -0,0 +1,19 @@
+name: build
+
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+    branches:
+    - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: Build
+      run: cargo build --verbose
+    - name: Run tests
+      run: cargo test --verbose
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..53eaa21
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/target
+**/*.rs.bk
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..33b0b15
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,24 @@
+[package]
+name = "mda"
+version = "0.1.0"
+authors = ["Alexandros Frantzis <alf82@freemail.gr>"]
+edition = "2018"
+description = "A library for creating custom Mail Delivery Agents"
+license = "MPL-2.0"
+repository = "https://github.com/afrantzis/mda-rs"
+documentation = "https://docs.rs/mda"
+homepage = "https://github.com/afrantzis/mda-rs"
+readme = "README.md"
+categories = ["email"]
+exclude = ["/.github/**"]
+
+[dependencies]
+regex = "1"
+libc = "0.2"
+gethostname = "0.2"
+memchr = "2.2"
+charset = "0.1"
+lazy_static = "1.4"
+
+[dev-dependencies]
+tempfile = "3"
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..14e2f77
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,373 @@
+Mozilla Public License Version 2.0
+==================================
+
+1. Definitions
+--------------
+
+1.1. "Contributor"
+    means each individual or legal entity that creates, contributes to
+    the creation of, or owns Covered Software.
+
+1.2. "Contributor Version"
+    means the combination of the Contributions of others (if any) used
+    by a Contributor and that particular Contributor's Contribution.
+
+1.3. "Contribution"
+    means Covered Software of a particular Contributor.
+
+1.4. "Covered Software"
+    means Source Code Form to which the initial Contributor has attached
+    the notice in Exhibit A, the Executable Form of such Source Code
+    Form, and Modifications of such Source Code Form, in each case
+    including portions thereof.
+
+1.5. "Incompatible With Secondary Licenses"
+    means
+
+    (a) that the initial Contributor has attached the notice described
+        in Exhibit B to the Covered Software; or
+
+    (b) that the Covered Software was made available under the terms of
+        version 1.1 or earlier of the License, but not also under the
+        terms of a Secondary License.
+
+1.6. "Executable Form"
+    means any form of the work other than Source Code Form.
+
+1.7. "Larger Work"
+    means a work that combines Covered Software with other material, in 
+    a separate file or files, that is not Covered Software.
+
+1.8. "License"
+    means this document.
+
+1.9. "Licensable"
+    means having the right to grant, to the maximum extent possible,
+    whether at the time of the initial grant or subsequently, any and
+    all of the rights conveyed by this License.
+
+1.10. "Modifications"
+    means any of the following:
+
+    (a) any file in Source Code Form that results from an addition to,
+        deletion from, or modification of the contents of Covered
+        Software; or
+
+    (b) any new file in Source Code Form that contains any Covered
+        Software.
+
+1.11. "Patent Claims" of a Contributor
+    means any patent claim(s), including without limitation, method,
+    process, and apparatus claims, in any patent Licensable by such
+    Contributor that would be infringed, but for the grant of the
+    License, by the making, using, selling, offering for sale, having
+    made, import, or transfer of either its Contributions or its
+    Contributor Version.
+
+1.12. "Secondary License"
+    means either the GNU General Public License, Version 2.0, the GNU
+    Lesser General Public License, Version 2.1, the GNU Affero General
+    Public License, Version 3.0, or any later versions of those
+    licenses.
+
+1.13. "Source Code Form"
+    means the form of the work preferred for making modifications.
+
+1.14. "You" (or "Your")
+    means an individual or a legal entity exercising rights under this
+    License. For legal entities, "You" includes any entity that
+    controls, is controlled by, or is under common control with You. For
+    purposes of this definition, "control" means (a) the power, direct
+    or indirect, to cause the direction or management of such entity,
+    whether by contract or otherwise, or (b) ownership of more than
+    fifty percent (50%) of the outstanding shares or beneficial
+    ownership of such entity.
+
+2. License Grants and Conditions
+--------------------------------
+
+2.1. Grants
+
+Each Contributor hereby grants You a world-wide, royalty-free,
+non-exclusive license:
+
+(a) under intellectual property rights (other than patent or trademark)
+    Licensable by such Contributor to use, reproduce, make available,
+    modify, display, perform, distribute, and otherwise exploit its
+    Contributions, either on an unmodified basis, with Modifications, or
+    as part of a Larger Work; and
+
+(b) under Patent Claims of such Contributor to make, use, sell, offer
+    for sale, have made, import, and otherwise transfer either its
+    Contributions or its Contributor Version.
+
+2.2. Effective Date
+
+The licenses granted in Section 2.1 with respect to any Contribution
+become effective for each Contribution on the date the Contributor first
+distributes such Contribution.
+
+2.3. Limitations on Grant Scope
+
+The licenses granted in this Section 2 are the only rights granted under
+this License. No additional rights or licenses will be implied from the
+distribution or licensing of Covered Software under this License.
+Notwithstanding Section 2.1(b) above, no patent license is granted by a
+Contributor:
+
+(a) for any code that a Contributor has removed from Covered Software;
+    or
+
+(b) for infringements caused by: (i) Your and any other third party's
+    modifications of Covered Software, or (ii) the combination of its
+    Contributions with other software (except as part of its Contributor
+    Version); or
+
+(c) under Patent Claims infringed by Covered Software in the absence of
+    its Contributions.
+
+This License does not grant any rights in the trademarks, service marks,
+or logos of any Contributor (except as may be necessary to comply with
+the notice requirements in Section 3.4).
+
+2.4. Subsequent Licenses
+
+No Contributor makes additional grants as a result of Your choice to
+distribute the Covered Software under a subsequent version of this
+License (see Section 10.2) or under the terms of a Secondary License (if
+permitted under the terms of Section 3.3).
+
+2.5. Representation
+
+Each Contributor represents that the Contributor believes its
+Contributions are its original creation(s) or it has sufficient rights
+to grant the rights to its Contributions conveyed by this License.
+
+2.6. Fair Use
+
+This License is not intended to limit any rights You have under
+applicable copyright doctrines of fair use, fair dealing, or other
+equivalents.
+
+2.7. Conditions
+
+Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted
+in Section 2.1.
+
+3. Responsibilities
+-------------------
+
+3.1. Distribution of Source Form
+
+All distribution of Covered Software in Source Code Form, including any
+Modifications that You create or to which You contribute, must be under
+the terms of this License. You must inform recipients that the Source
+Code Form of the Covered Software is governed by the terms of this
+License, and how they can obtain a copy of this License. You may not
+attempt to alter or restrict the recipients' rights in the Source Code
+Form.
+
+3.2. Distribution of Executable Form
+
+If You distribute Covered Software in Executable Form then:
+
+(a) such Covered Software must also be made available in Source Code
+    Form, as described in Section 3.1, and You must inform recipients of
+    the Executable Form how they can obtain a copy of such Source Code
+    Form by reasonable means in a timely manner, at a charge no more
+    than the cost of distribution to the recipient; and
+
+(b) You may distribute such Executable Form under the terms of this
+    License, or sublicense it under different terms, provided that the
+    license for the Executable Form does not attempt to limit or alter
+    the recipients' rights in the Source Code Form under this License.
+
+3.3. Distribution of a Larger Work
+
+You may create and distribute a Larger Work under terms of Your choice,
+provided that You also comply with the requirements of this License for
+the Covered Software. If the Larger Work is a combination of Covered
+Software with a work governed by one or more Secondary Licenses, and the
+Covered Software is not Incompatible With Secondary Licenses, this
+License permits You to additionally distribute such Covered Software
+under the terms of such Secondary License(s), so that the recipient of
+the Larger Work may, at their option, further distribute the Covered
+Software under the terms of either this License or such Secondary
+License(s).
+
+3.4. Notices
+
+You may not remove or alter the substance of any license notices
+(including copyright notices, patent notices, disclaimers of warranty,
+or limitations of liability) contained within the Source Code Form of
+the Covered Software, except that You may alter any license notices to
+the extent required to remedy known factual inaccuracies.
+
+3.5. Application of Additional Terms
+
+You may choose to offer, and to charge a fee for, warranty, support,
+indemnity or liability obligations to one or more recipients of Covered
+Software. However, You may do so only on Your own behalf, and not on
+behalf of any Contributor. You must make it absolutely clear that any
+such warranty, support, indemnity, or liability obligation is offered by
+You alone, and You hereby agree to indemnify every Contributor for any
+liability incurred by such Contributor as a result of warranty, support,
+indemnity or liability terms You offer. You may include additional
+disclaimers of warranty and limitations of liability specific to any
+jurisdiction.
+
+4. Inability to Comply Due to Statute or Regulation
+---------------------------------------------------
+
+If it is impossible for You to comply with any of the terms of this
+License with respect to some or all of the Covered Software due to
+statute, judicial order, or regulation then You must: (a) comply with
+the terms of this License to the maximum extent possible; and (b)
+describe the limitations and the code they affect. Such description must
+be placed in a text file included with all distributions of the Covered
+Software under this License. Except to the extent prohibited by statute
+or regulation, such description must be sufficiently detailed for a
+recipient of ordinary skill to be able to understand it.
+
+5. Termination
+--------------
+
+5.1. The rights granted under this License will terminate automatically
+if You fail to comply with any of its terms. However, if You become
+compliant, then the rights granted under this License from a particular
+Contributor are reinstated (a) provisionally, unless and until such
+Contributor explicitly and finally terminates Your grants, and (b) on an
+ongoing basis, if such Contributor fails to notify You of the
+non-compliance by some reasonable means prior to 60 days after You have
+come back into compliance. Moreover, Your grants from a particular
+Contributor are reinstated on an ongoing basis if such Contributor
+notifies You of the non-compliance by some reasonable means, this is the
+first time You have received notice of non-compliance with this License
+from such Contributor, and You become compliant prior to 30 days after
+Your receipt of the notice.
+
+5.2. If You initiate litigation against any entity by asserting a patent
+infringement claim (excluding declaratory judgment actions,
+counter-claims, and cross-claims) alleging that a Contributor Version
+directly or indirectly infringes any patent, then the rights granted to
+You by any and all Contributors for the Covered Software under Section
+2.1 of this License shall terminate.
+
+5.3. In the event of termination under Sections 5.1 or 5.2 above, all
+end user license agreements (excluding distributors and resellers) which
+have been validly granted by You or Your distributors under this License
+prior to termination shall survive termination.
+
+************************************************************************
+*                                                                      *
+*  6. Disclaimer of Warranty                                           *
+*  -------------------------                                           *
+*                                                                      *
+*  Covered Software is provided under this License on an "as is"       *
+*  basis, without warranty of any kind, either expressed, implied, or  *
+*  statutory, including, without limitation, warranties that the       *
+*  Covered Software is free of defects, merchantable, fit for a        *
+*  particular purpose or non-infringing. The entire risk as to the     *
+*  quality and performance of the Covered Software is with You.        *
+*  Should any Covered Software prove defective in any respect, You     *
+*  (not any Contributor) assume the cost of any necessary servicing,   *
+*  repair, or correction. This disclaimer of warranty constitutes an   *
+*  essential part of this License. No use of any Covered Software is   *
+*  authorized under this License except under this disclaimer.         *
+*                                                                      *
+************************************************************************
+
+************************************************************************
+*                                                                      *
+*  7. Limitation of Liability                                          *
+*  --------------------------                                          *
+*                                                                      *
+*  Under no circumstances and under no legal theory, whether tort      *
+*  (including negligence), contract, or otherwise, shall any           *
+*  Contributor, or anyone who distributes Covered Software as          *
+*  permitted above, be liable to You for any direct, indirect,         *
+*  special, incidental, or consequential damages of any character      *
+*  including, without limitation, damages for lost profits, loss of    *
+*  goodwill, work stoppage, computer failure or malfunction, or any    *
+*  and all other commercial damages or losses, even if such party      *
+*  shall have been informed of the possibility of such damages. This   *
+*  limitation of liability shall not apply to liability for death or   *
+*  personal injury resulting from such party's negligence to the       *
+*  extent applicable law prohibits such limitation. Some               *
+*  jurisdictions do not allow the exclusion or limitation of           *
+*  incidental or consequential damages, so this exclusion and          *
+*  limitation may not apply to You.                                    *
+*                                                                      *
+************************************************************************
+
+8. Litigation
+-------------
+
+Any litigation relating to this License may be brought only in the
+courts of a jurisdiction where the defendant maintains its principal
+place of business and such litigation shall be governed by laws of that
+jurisdiction, without reference to its conflict-of-law provisions.
+Nothing in this Section shall prevent a party's ability to bring
+cross-claims or counter-claims.
+
+9. Miscellaneous
+----------------
+
+This License represents the complete agreement concerning the subject
+matter hereof. If any provision of this License is held to be
+unenforceable, such provision shall be reformed only to the extent
+necessary to make it enforceable. Any law or regulation which provides
+that the language of a contract shall be construed against the drafter
+shall not be used to construe this License against a Contributor.
+
+10. Versions of the License
+---------------------------
+
+10.1. New Versions
+
+Mozilla Foundation is the license steward. Except as provided in Section
+10.3, no one other than the license steward has the right to modify or
+publish new versions of this License. Each version will be given a
+distinguishing version number.
+
+10.2. Effect of New Versions
+
+You may distribute the Covered Software under the terms of the version
+of the License under which You originally received the Covered Software,
+or under the terms of any subsequent version published by the license
+steward.
+
+10.3. Modified Versions
+
+If you create software not governed by this License, and you want to
+create a new license for such software, you may create and use a
+modified version of this License if you rename the license and remove
+any references to the name of the license steward (except to note that
+such modified license differs from this License).
+
+10.4. Distributing Source Code Form that is Incompatible With Secondary
+Licenses
+
+If You choose to distribute Source Code Form that is Incompatible With
+Secondary Licenses under the terms of this version of the License, the
+notice described in Exhibit B of this License must be attached.
+
+Exhibit A - Source Code Form License Notice
+-------------------------------------------
+
+  This Source Code Form is subject to the terms of the Mozilla Public
+  License, v. 2.0. If a copy of the MPL was not distributed with this
+  file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+If it is not possible or desirable to put the notice in a particular
+file, then You may include the notice in a location (such as a LICENSE
+file in a relevant directory) where a recipient would be likely to look
+for such a notice.
+
+You may add additional accurate notices of copyright ownership.
+
+Exhibit B - "Incompatible With Secondary Licenses" Notice
+---------------------------------------------------------
+
+  This Source Code Form is "Incompatible With Secondary Licenses", as
+  defined by the Mozilla Public License, v. 2.0.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..f757ae6
--- /dev/null
+++ b/README.md
@@ -0,0 +1,35 @@
+mda-rs
+======
+
+mda-rs is a Rust library for writing custom Mail Deliver Agents.
+
+![](https://github.com/afrantzis/mda-rs/workflows/build/badge.svg)
+
+### Documentation
+
+The detailed module documentation, including code examples for all features,
+can be found at [https://docs.rs/mda](https://docs.rs/mda).
+
+### Usage
+
+Add this to your `Cargo.toml`:
+
+```toml
+[dependencies]
+mda = "0.1"
+```
+
+If you are using Rust 2015 add the following to your crate root file (Rust 2018
+doesn't require this):
+
+```rust
+extern crate mda;
+```
+
+See [examples/personal-mda.rs](examples/personal-mda.rs) for an example that
+uses mda-rs.
+
+### License
+
+This project is licensed under the Mozilla Public License Version 2.0
+([LICENSE](LICENSE) or https://www.mozilla.org/en-US/MPL/2.0/).
diff --git a/examples/normalize.rs b/examples/normalize.rs
new file mode 100644
index 0000000..359250a
--- /dev/null
+++ b/examples/normalize.rs
@@ -0,0 +1,18 @@
+// Copyright 2019 Alexandros Frantzis
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+//
+// SPDX-License-Identifier: MPL-2.0
+
+//! Writes out the normalized form of an email.
+
+use std::io::{self, Write};
+use mda::{Email, Result};
+
+fn main() -> Result<()> {
+    let email = Email::from_stdin()?;
+    io::stdout().lock().write_all(email.data())?;
+    Ok(())
+}
diff --git a/examples/personal-mda.rs b/examples/personal-mda.rs
new file mode 100644
index 0000000..aa26431
--- /dev/null
+++ b/examples/personal-mda.rs
@@ -0,0 +1,55 @@
+// Copyright 2019 Alexandros Frantzis
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+//
+// SPDX-License-Identifier: MPL-2.0
+
+//! An example of a custom MDA.
+
+use std::path::PathBuf;
+
+use mda::{Email, EmailRegex, Result, DeliveryDurability};
+
+fn main() -> Result<()> {
+    // Just some random path to make it highly unlikely that this example will
+    // indvertently mess up something.
+    let root = PathBuf::from("/tmp/my-personal-mail-96f29eb6375cfa37");
+
+    // If we are sure bogofilter is available, the below can be better written as:
+    // let mut email = Email::from_stdin_filtered(&["/usr/bin/bogofilter", "-ep"])?;
+    let mut email = Email::from_stdin()?;
+    if let Ok(new_email) = email.filter(&["/usr/bin/bogofilter", "-ep"]) {
+        email = new_email;
+    }
+
+    // Quicker (but possibly less durable) delivery.
+    email.set_delivery_durability(DeliveryDurability::FileSyncOnly);
+
+    let from = email.header_field("From").unwrap_or("");
+    let bogosity = email.header_field("X-Bogosity").unwrap_or("");
+
+    if bogosity.contains("Spam, tests=bogofilter") ||
+       from.contains("@banneddomain.com") {
+        email.deliver_to_maildir(root.join("spam"))?;
+        return Ok(());
+    }
+
+    let cc = email.header_field("Cc").unwrap_or("");
+    let to = email.header_field("To").unwrap_or("");
+
+    if to.contains("myworkemail@example.com") ||
+       cc.contains("myworkemail@example.com") {
+        if email.body().search("URGENCY RATING: (CRITICAL|URGENT)")? {
+            email.deliver_to_maildir(root.join("inbox/myemail/urgent"))?;
+        } else {
+            email.deliver_to_maildir(root.join("inbox/myemail/normal"))?;
+        }
+        return Ok(());
+    }
+
+    email.deliver_to_maildir(root.join("inbox/unsorted"))?;
+
+    Ok(())
+}
diff --git a/src/decode.rs b/src/decode.rs
new file mode 100644
index 0000000..8004f18
--- /dev/null
+++ b/src/decode.rs
@@ -0,0 +1,224 @@
+// Copyright 2019 Alexandros Frantzis
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+//
+// SPDX-License-Identifier: MPL-2.0
+
+//! Base64 and quoted-printable decoding.
+
+use crate::Result;
+
+const PAD: u8 = 64; // The pseudo-index of the PAD character.
+const INV: u8 = 99; // An invalid index.
+
+static BASE64_INDICES: &'static [u8] = &[
+     //   0    1    2    3    4    5    6    7    8    9    A    B    C    D    E    F
+/* 0 */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,
+/* 1 */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,
+/* 2 */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,  62, INV, INV, INV,  63,
+/* 3 */  52,  53,  54,  55,  56,  57,  58,  59,  60,  61, INV, INV, INV, PAD, INV, INV,
+/* 4 */ INV,   0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,
+/* 5 */  15,  16,  17,  18,  19,  20,  21,  22,  23,  24,  25, INV, INV, INV, INV, INV,
+/* 6 */ INV,  26,  27,  28,  29,  30,  31,  32,  33,  34,  35,  36,  37,  38,  39,  40,
+/* 7 */  41,  42,  43,  44,  45,  46,  47,  48,  49,  50,  51, INV, INV, INV, INV, INV,
+/* 8 */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,
+/* 9 */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,
+/* A */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,
+/* B */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,
+/* C */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,
+/* D */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,
+/* E */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,
+/* F */ INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV, INV,
+];
+
+/// Decodes base64 encoded data, appending the decoded data to a Vec<u8>.
+///
+/// During decoding all line breaks and invalid characters are ignored.
+/// If an error is encountered during decoding, the already decoded data in the
+/// output buffer is left intact. It's up to the caller to deal with the partial
+/// decoded data in case of failure.
+pub fn base64_decode_into_buf(input: &[u8], output: &mut Vec<u8>) -> Result<()> {
+    let mut num_chars = 0;
+    let mut cur_triplet = 0;
+    let mut valid_chars = 0;
+
+    for c in input {
+        let ci = BASE64_INDICES[*c as usize];
+        match ci {
+            // rfc2045: All line breaks or other characters not
+            // found in Table 1 must be ignored by decoding software.
+            INV => continue,
+            _ if ci < PAD => valid_chars += 1,
+            _ => {}
+        }
+
+        cur_triplet = cur_triplet << 6 | ((ci & 0x3f) as u32);
+        num_chars += 1;
+
+        if num_chars == 4 {
+            match valid_chars {
+                2 => output.push((cur_triplet >> 16) as u8),
+                3 => output.extend(
+                    &[(cur_triplet >> 16) as u8, (cur_triplet >> 8) as u8]
+                ),
+                4 => output.extend(
+                    &[(cur_triplet >> 16) as u8,
+                      (cur_triplet >> 8) as u8,
+                      cur_triplet as u8
+                    ]
+                ),
+                _ => return Err("Invalid base64 encoding".into()),
+            }
+
+            cur_triplet = 0;
+            num_chars = 0;
+            valid_chars = 0;
+        }
+    }
+
+    // rfc2045: A full encoding quantum is always completed at the end of a body.
+    if num_chars != 0 {
+        return Err("Unpadded input".into());
+    }
+
+    Ok(())
+}
+
+/// Converts an ascii byte representing a hex digit to it's numerical value.
+fn hexdigit_to_num(mut a: u8) -> Option<u8> {
+    if a.is_ascii_digit() {
+        return Some(a - b'0');
+    }
+
+    a.make_ascii_lowercase();
+
+    if a >= b'a' && a <= b'f' {
+        return Some(a - b'a' + 10);
+    }
+
+    None
+}
+
+/// Decodes quoted-printable encoded data, appending the decoding data to a
+/// Vec<u8>.
+///
+/// During decoding all line breaks and invalid characters are ignored.
+/// If an error is encountered during decoding, the already decoded data in the
+/// output buffer is left intact. It's up to the caller to deal with the partial
+/// decoded data in case of failure.
+pub fn qp_decode_into_buf(input: &[u8], output: &mut Vec<u8>) -> Result<()> {
+    let mut iter = input.iter().peekable();
+
+    'outer: loop {
+        loop {
+            match iter.next() {
+                Some(b'=') => break,
+                Some(c) => output.push(*c),
+                None => break 'outer,
+            }
+        }
+
+        // At this point we have encountered a '=', so check
+        // to see what follows.
+        if let Some(&first) = iter.next() {
+            // A CRLF/LF after '=' marks a line continuation, and
+            // is effectively dropped.
+            if first == b'\r' {
+                if iter.peek() == Some(&&b'\n') {
+                    iter.next();
+                    continue;
+                }
+            } else if first == b'\n' {
+                continue;
+            } else if let Some(first_num) = hexdigit_to_num(first) {
+                // A valid pair of hexdigits represent the raw byte value.
+                if let Some(&&second) = iter.peek() {
+                    if let Some(second_num) = hexdigit_to_num(second) {
+                        output.push(first_num * 16 + second_num);
+                        iter.next();
+                        continue;
+                    }
+                }
+            }
+
+            // Emit the raw sequence if it's not one of the special
+            // special cases checked above.
+            output.extend(&[b'=', first]);
+        } else {
+            // Last character in the input was an '=', just emit it.
+            output.push(b'=');
+        }
+    }
+
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod test_base64 {
+    use crate::decode::base64_decode_into_buf;
+
+    #[test]
+    fn decodes_full_length() {
+        let mut decoded = Vec::new();
+        assert!(base64_decode_into_buf("YWJj".as_bytes(), &mut decoded).is_ok());
+        assert_eq!(decoded, &[b'a', b'b', b'c']);
+    }
+
+    #[test]
+    fn decodes_with_two_padding() {
+        let mut decoded = Vec::new();
+        assert!(base64_decode_into_buf("YWJjZA==".as_bytes(), &mut decoded).is_ok());
+        assert_eq!(decoded, &[b'a', b'b', b'c', b'd']);
+    }
+
+    #[test]
+    fn decodes_with_one_padding() {
+        let mut decoded = Vec::new();
+        assert!(base64_decode_into_buf("YWJjZGU=".as_bytes(), &mut decoded).is_ok());
+        assert_eq!(decoded, &[b'a', b'b', b'c', b'd', b'e']);
+    }
+
+    #[test]
+    fn error_with_invalid_paddings() {
+        let mut decoded = Vec::new();
+        assert!(base64_decode_into_buf("YWJj====".as_bytes(), &mut decoded).is_err());
+        assert!(base64_decode_into_buf("YWJjZ===".as_bytes(), &mut decoded).is_err());
+        assert!(base64_decode_into_buf("====".as_bytes(), &mut decoded).is_err());
+    }
+
+    #[test]
+    fn error_with_unpadded_input() {
+        let mut decoded = Vec::new();
+        assert!(base64_decode_into_buf("YWJjZA=".as_bytes(), &mut decoded).is_err());
+    }
+}
+
+#[cfg(test)]
+mod test_qp {
+    use crate::decode::qp_decode_into_buf;
+
+    #[test]
+    fn decodes_byte() {
+        let mut decoded = Vec::new();
+        assert!(qp_decode_into_buf("a=62c=64".as_bytes(), &mut decoded).is_ok());
+        assert_eq!(decoded, &[b'a', b'b', b'c', b'd']);
+    }
+
+    #[test]
+    fn decodes_soft_break() {
+        let mut decoded = Vec::new();
+        assert!(qp_decode_into_buf("a=\r\nb=\nc".as_bytes(), &mut decoded).is_ok());
+        assert_eq!(decoded, &[b'a', b'b', b'c']);
+    }
+
+    #[test]
+    fn invalid_sequences_are_untouched() {
+        let mut decoded = Vec::new();
+        let invalid_sequence = "a=6t= c=".as_bytes();
+        assert!(qp_decode_into_buf(invalid_sequence, &mut decoded).is_ok());
+        assert_eq!(decoded, invalid_sequence);
+    }
+}
diff --git a/src/deliver.rs b/src/deliver.rs
new file mode 100644
index 0000000..8ade10f
--- /dev/null
+++ b/src/deliver.rs
@@ -0,0 +1,176 @@
+// Copyright 2019 Alexandros Frantzis
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+//
+// SPDX-License-Identifier: MPL-2.0
+
+//! Email delivery functionality.
+
+use std::fs::{self, File};
+use std::io::ErrorKind;
+use std::io::prelude::*;
+use std::os::unix::prelude::*;
+use std::path::{PathBuf, Path};
+use std::process;
+use std::sync::{Arc, Mutex};
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use crate::{DeliveryDurability, Result};
+
+use gethostname::gethostname;
+use libc;
+
+/// A generator for likely unique maildir email filenames.
+///
+/// Using it as an iterator gets a filename that can be used in a maildir
+/// and is likely to be unique.
+pub struct EmailFilenameGenerator {
+    count: usize,
+    max_seen_unix_time: u64,
+    hostname: String,
+}
+
+impl EmailFilenameGenerator {
+    pub fn new() -> Self {
+        // From https://cr.yp.to/proto/maildir.html:
+        // "To deal with invalid host names, replace / with \057 and : with \072"
+        let hostname =
+            gethostname()
+                .to_string_lossy()
+                .into_owned()
+                .replace("/", r"\057")
+                .replace(":", r"\072");
+
+        EmailFilenameGenerator{
+            count: 0,
+            max_seen_unix_time: 0,
+            hostname: hostname,
+        }
+    }
+}
+
+impl Iterator for EmailFilenameGenerator {
+    type Item = String;
+
+    fn next(&mut self) -> Option<String> {
+        let unix_time = SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs();
+        let pid = process::id();
+
+        if self.max_seen_unix_time < unix_time {
+            self.max_seen_unix_time = unix_time;
+            self.count = 0;
+        } else {
+            self.count += 1;
+        }
+
+        Some(format!("{}.{}_{}.{}", unix_time, pid, self.count, self.hostname))
+    }