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Diffstat (limited to 'core/src/mime.rs')
| -rw-r--r-- | core/src/mime.rs | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/core/src/mime.rs b/core/src/mime.rs new file mode 100644 index 0000000..7897fe7 --- /dev/null +++ b/core/src/mime.rs @@ -0,0 +1,121 @@ +//! Module containing some utilities for MIME usage/creation. +use rand::{self, Rng}; + + + +// The maximal boundary with wich " boundary=\"...\"" fits into 78 chars line length limit +const MULTIPART_BOUNDARY_MAX_LENGTH: usize = 66; + +// Does not include ' ' to remove special handling for last char. +static BOUNDARY_CHARS: &[char] = &[ + '\'', + '(', ')', '+', ',', '-', '.', '/', + '0', '1', '2', '3', '4', '5', '6', '7', + '8', '9', ':', '=', '?', + 'A', 'B', 'C', 'D', 'E', 'F', 'G', + 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', + 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', + 'X', 'Y', 'Z', '_', + 'a', 'b', 'c', 'd', 'e', 'f', 'g', + 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', + 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', + 'x', 'y', 'z', +]; + +/// Prevent collisions with Base64/Quoted-Printable +static ANTI_COLLISION_CHARS: &str = "=_^"; + +/// Generate a boundary from a counter, "=_^" and a random sequence of boundary chars. +/// +/// # Usage Note +/// +/// _Be aware that it might be required to quote the boundary._ +/// +/// # Implementation Details +/// +/// The boundary will start with `=_^` which is neither valid for base64 nor +/// quoted-printable encoding followed by a hex repr. of the given count, +/// a `.` and a random sequence of boundary chars. +/// +/// The boundary will be 66 chars long, this is so that if a boundary parameter is +/// placed on it's own line it won't be more then 78 chars. (66 chars boundary, +/// + 2 chars quotation + 9 chars for 'boundary=' + 1 char because of `\r\n<WS>` +/// == 78 chars) +/// +/// The remaining characters will be picked based one the grammar defined in rfc2046, +/// which relevant part is: +/// +/// ```BNF +/// boundary := 0*69<bchars> bcharsnospace +/// bchars := bcharsnospace / " " +/// bcharsnospace := DIGIT / ALPHA / "'" / "(" / ")" / +/// "+" / "_" / "," / "-" / "." / +/// "/" / ":" / "=" / "?" +/// ``` +/// +/// Note that `' '` isn't used for simplicity. +/// +pub fn create_structured_random_boundary(count: usize) -> String { + let mut out = format!("{anti_collision}{count:x}.", + anti_collision=ANTI_COLLISION_CHARS, + count=count + ); + + let rem = MULTIPART_BOUNDARY_MAX_LENGTH-out.len(); + out.reserve(rem); + + let mut rng = rand::thread_rng(); + let len = BOUNDARY_CHARS.len(); + for _ in 0..rem { + let idx = rng.gen_range(0, len); + out.push(BOUNDARY_CHARS[idx]); + } + + out +} + + +#[cfg(test)] +mod test { + + mod write_random_boundary_to { + use super::super::*; + + #[test] + fn boundary_is_not_quoted() { + let out = create_structured_random_boundary(0); + assert!(!out.starts_with("\"")); + assert!(!out.ends_with("\"")); + } + + #[test] + fn boundary_start_special() { + let out = create_structured_random_boundary(0); + assert!(out.starts_with("=_^0.")); + } + + #[test] + fn boundary_has_a_resonable_length() { + let out = create_structured_random_boundary(0); + assert!(out.len() > 22 && out.len() <= MULTIPART_BOUNDARY_MAX_LENGTH); + let out = create_structured_random_boundary(1000); + assert!(out.len() > 22 && out.len() <= MULTIPART_BOUNDARY_MAX_LENGTH); + } + + #[test] + fn boundary_does_not_contain_space_or_slach_or_quotes() { + // while it could contain them it's recommended not to do it + let out = create_structured_random_boundary(0); + + for ch in out[1..out.len()-1].chars() { + assert!(ch as u32 >= 32); + assert!(ch as u32 <= 126); + assert_ne!(ch, '\t'); + assert_ne!(ch, '\\'); + assert_ne!(ch, '"'); + } + + assert_ne!(out.as_bytes()[out.len()-1], b' '); + } + } +}
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