modularized all source code (#4391)

* modularized all external plugins

* added README.md in plugins

* fixed title

* fixed typo

* relative link to external plugins

* external plugins configuration README

* added plugins link

* remove plugins link

* plugin names are links

* added links to external plugins

* removed unecessary spacing

* list to table

* added language

* fixed typo

* list to table on internal plugins

* added more documentation to internal plugins

* moved python, node, and bash code and configs into the external plugins

* added statsd README

* fix bug with corrupting config.h every 2nd compilation

* moved all config files together with their code

* more documentation

* diskspace info

* fixed broken links in apps.plugin

* added backends docs

* updated plugins readme

* move nc-backend.sh to backends

* created daemon directory

* moved all code outside src/

* fixed readme identation

* renamed plugins.d.plugin to plugins.d

* updated readme

* removed linux- from linux plugins

* updated readme

* updated readme

* updated readme

* updated readme

* updated readme

* updated readme

* fixed README.md links

* fixed netdata tree links

* updated codacy, codeclimate and lgtm excluded paths

* update CMakeLists.txt

* updated automake options at top directory

* libnetdata slit into directories

* updated READMEs

* updated READMEs

* updated ARL docs

* updated ARL docs

* moved /plugins to /collectors

* moved all external plugins outside plugins.d

* updated codacy, codeclimate, lgtm

* updated README

* updated url

* updated readme

* updated readme

* updated readme

* updated readme

* moved api and web into webserver

* web/api web/gui web/server

* modularized webserver

* removed web/gui/version.txt

4 files changed, 233 insertions, 0 deletions

diff --git a/libnetdata/popen/Makefile.am b/libnetdata/popen/Makefile.am
new file mode 100644
index 0000000000..1cb69ed99a
--- /dev/null
+++ b/libnetdata/popen/Makefile.am
@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+AUTOMAKE_OPTIONS = subdir-objects
+MAINTAINERCLEANFILES = $(srcdir)/Makefile.in
+
+
+dist_noinst_DATA = \
+	README.md \
+	$(NULL)
diff --git a/libnetdata/popen/README.md b/libnetdata/popen/README.md
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/libnetdata/popen/README.md
diff --git a/libnetdata/popen/popen.c b/libnetdata/popen/popen.c
new file mode 100644
index 0000000000..845363fd22
--- /dev/null
+++ b/libnetdata/popen/popen.c
@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "../libnetdata.h"
+
+/*
+struct mypopen {
+    pid_t pid;
+    FILE *fp;
+    struct mypopen *next;
+    struct mypopen *prev;
+};
+
+static struct mypopen *mypopen_root = NULL;
+
+static void mypopen_add(FILE *fp, pid_t *pid) {
+    struct mypopen *mp = malloc(sizeof(struct mypopen));
+    if(!mp) {
+        fatal("Cannot allocate %zu bytes", sizeof(struct mypopen))
+        return;
+    }
+
+    mp->fp = fp;
+    mp->pid = pid;
+    mp->next = popen_root;
+    mp->prev = NULL;
+    if(mypopen_root) mypopen_root->prev = mp;
+    mypopen_root = mp;
+}
+
+static void mypopen_del(FILE *fp) {
+    struct mypopen *mp;
+
+    for(mp = mypopen_root; mp; mp = mp->next)
+        if(mp->fd == fp) break;
+
+    if(!mp) error("Cannot find mypopen() file pointer in open childs.");
+    else {
+        if(mp->next) mp->next->prev = mp->prev;
+        if(mp->prev) mp->prev->next = mp->next;
+        if(mypopen_root == mp) mypopen_root = mp->next;
+        free(mp);
+    }
+}
+*/
+#define PIPE_READ 0
+#define PIPE_WRITE 1
+
+FILE *mypopen(const char *command, volatile pid_t *pidptr)
+{
+    int pipefd[2];
+
+    if(pipe(pipefd) == -1) return NULL;
+
+    int pid = fork();
+    if(pid == -1) {
+        close(pipefd[PIPE_READ]);
+        close(pipefd[PIPE_WRITE]);
+        return NULL;
+    }
+    if(pid != 0) {
+        // the parent
+        *pidptr = pid;
+        close(pipefd[PIPE_WRITE]);
+        FILE *fp = fdopen(pipefd[PIPE_READ], "r");
+        /*mypopen_add(fp, pid);*/
+        return(fp);
+    }
+    // the child
+
+    // close all files
+    int i;
+    for(i = (int) (sysconf(_SC_OPEN_MAX) - 1); i >= 0; i--)
+        if(i != STDIN_FILENO && i != STDERR_FILENO && i != pipefd[PIPE_WRITE]) close(i);
+
+    // move the pipe to stdout
+    if(pipefd[PIPE_WRITE] != STDOUT_FILENO) {
+        dup2(pipefd[PIPE_WRITE], STDOUT_FILENO);
+        close(pipefd[PIPE_WRITE]);
+    }
+
+#ifdef DETACH_PLUGINS_FROM_NETDATA
+    // this was an attempt to detach the child and use the suspend mode charts.d
+    // unfortunatelly it does not work as expected.
+
+    // fork again to become session leader
+    pid = fork();
+    if(pid == -1)
+        error("pre-execution of command '%s' on pid %d: Cannot fork 2nd time.", command, getpid());
+
+    if(pid != 0) {
+        // the parent
+        exit(0);
+    }
+
+    // set a new process group id for just this child
+    if( setpgid(0, 0) != 0 )
+        error("pre-execution of command '%s' on pid %d: Cannot set a new process group.", command, getpid());
+
+    if( getpgid(0) != getpid() )
+        error("pre-execution of command '%s' on pid %d: Cannot set a new process group. Process group set is incorrect. Expected %d, found %d", command, getpid(), getpid(), getpgid(0));
+
+    if( setsid() != 0 )
+        error("pre-execution of command '%s' on pid %d: Cannot set session id.", command, getpid());
+
+    fprintf(stdout, "MYPID %d\n", getpid());
+    fflush(NULL);
+#endif
+
+    // reset all signals
+    signals_unblock();
+    signals_reset();
+
+    debug(D_CHILDS, "executing command: '%s' on pid %d.", command, getpid());
+    execl("/bin/sh", "sh", "-c", command, NULL);
+    exit(1);
+}
+
+FILE *mypopene(const char *command, volatile pid_t *pidptr, char **env) {
+    int pipefd[2];
+
+    if(pipe(pipefd) == -1)
+        return NULL;
+
+    int pid = fork();
+    if(pid == -1) {
+        close(pipefd[PIPE_READ]);
+        close(pipefd[PIPE_WRITE]);
+        return NULL;
+    }
+    if(pid != 0) {
+        // the parent
+        *pidptr = pid;
+        close(pipefd[PIPE_WRITE]);
+        FILE *fp = fdopen(pipefd[PIPE_READ], "r");
+        return(fp);
+    }
+    // the child
+
+    // close all files
+    int i;
+    for(i = (int) (sysconf(_SC_OPEN_MAX) - 1); i >= 0; i--)
+        if(i != STDIN_FILENO && i != STDERR_FILENO && i != pipefd[PIPE_WRITE]) close(i);
+
+    // move the pipe to stdout
+    if(pipefd[PIPE_WRITE] != STDOUT_FILENO) {
+        dup2(pipefd[PIPE_WRITE], STDOUT_FILENO);
+        close(pipefd[PIPE_WRITE]);
+    }
+
+    execle("/bin/sh", "sh", "-c", command, NULL, env);
+    exit(1);
+}
+
+int mypclose(FILE *fp, pid_t pid) {
+    debug(D_EXIT, "Request to mypclose() on pid %d", pid);
+
+    /*mypopen_del(fp);*/
+
+    // close the pipe fd
+    // this is required in musl
+    // without it the childs do not exit
+    close(fileno(fp));
+
+    // close the pipe file pointer
+    fclose(fp);
+
+    errno = 0;
+
+    siginfo_t info;
+    if(waitid(P_PID, (id_t) pid, &info, WEXITED) != -1) {
+        switch(info.si_code) {
+            case CLD_EXITED:
+                if(info.si_status)
+                    error("child pid %d exited with code %d.", info.si_pid, info.si_status);
+                return(info.si_status);
+
+            case CLD_KILLED:
+                error("child pid %d killed by signal %d.", info.si_pid, info.si_status);
+                return(-1);
+
+            case CLD_DUMPED:
+                error("child pid %d core dumped by signal %d.", info.si_pid, info.si_status);
+                return(-2);
+
+            case CLD_STOPPED:
+                error("child pid %d stopped by signal %d.", info.si_pid, info.si_status);
+                return(0);
+
+            case CLD_TRAPPED:
+                error("child pid %d trapped by signal %d.", info.si_pid, info.si_status);
+                return(-4);
+
+            case CLD_CONTINUED:
+                error("child pid %d continued by signal %d.", info.si_pid, info.si_status);
+                return(0);
+
+            default:
+                error("child pid %d gave us a SIGCHLD with code %d and status %d.", info.si_pid, info.si_code, info.si_status);
+                return(-5);
+        }
+    }
+    else
+        error("Cannot waitid() for pid %d", pid);
+    
+    return 0;
+}
diff --git a/libnetdata/popen/popen.h b/libnetdata/popen/popen.h
new file mode 100644
index 0000000000..90d4b829b0
--- /dev/null
+++ b/libnetdata/popen/popen.h
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#ifndef NETDATA_POPEN_H
+#define NETDATA_POPEN_H 1
+
+#include "../libnetdata.h"
+
+#define PIPE_READ 0
+#define PIPE_WRITE 1
+
+extern FILE *mypopen(const char *command, volatile pid_t *pidptr);
+extern FILE *mypopene(const char *command, volatile pid_t *pidptr, char **env);
+extern int mypclose(FILE *fp, pid_t pid);
+
+extern void signals_unblock(void);
+extern void signals_reset(void);
+
+#endif /* NETDATA_POPEN_H */