gemscgi.c

   1 /* Copyright 2021, Martin Bays <mbays@sdf.org>
   2  * SPDX-License-Identifier: GPL-3.0-or-later */
   3 #include <stdbool.h>
   4 #include <stdio.h>
   5 #include <stdlib.h>
   6 #include <string.h>
   7 #include <sys/socket.h>
   8 #include <sys/types.h>
   9 #include <sys/un.h>
  10 #include <unistd.h>
  11
  12 #include "gemscgi.h"
  13
  14 /* Decode percent-escapes in place */
  15 static void urldecode(char *p) {
  16     char *w = p;
  17     bool escaped = false;
  18
  19     while (*p) {
  20         if (*p == '%') {
  21             escaped = true;
  22             ++p;
  23             if (sscanf(p, "%2hhx", w) == 1) {
  24                 ++w;
  25                 p+=2;
  26             }
  27         } else {
  28             if (escaped) *w = *p;
  29             ++p;
  30             ++w;
  31         }
  32     }
  33     *w = 0;
  34 }
  35
  36 #define MAX_REQUEST_SZ 4096
  37 /* Parse SCGI request with null body from fd s and place gemini-relevant
  38  * header values in request_info.
  39  * Return false on failure. */
  40 static bool parse_SCGI(int s, Request_Info *request_info)
  41 {
  42     char buf[MAX_REQUEST_SZ];
  43     int r = 0;
  44     while (1) {
  45         int r2 = read(s, buf + r, MAX_REQUEST_SZ - r);
  46         if (r2 <= 0) {
  47             perror("read");
  48             return false;
  49         }
  50         r += r2;
  51
  52         int sz;
  53         if (sscanf(buf, "%u:", &sz) == 1) {
  54             char buf2[16];
  55             snprintf(buf2, 16, "%u:,", sz);
  56             const int full_sz = sz + strlen(buf2);
  57
  58             if (full_sz > MAX_REQUEST_SZ) {
  59                 fprintf(stderr, "Bad request: Oversized, %u\n", sz);
  60                 return false;
  61             }
  62
  63             if (r == full_sz) {
  64                 break;
  65             }
  66
  67             if (r > full_sz) {
  68                 fprintf(stderr, "Bad request: non-empty body.\n");
  69                 return false;
  70             }
  71         }
  72     }
  73
  74     const char* end = &buf[r-1];
  75
  76     if (r <= 2) {
  77         /* Null request */
  78     } else if (buf[r-1] != ',' || buf[r-2] != 0) {
  79         fprintf(stderr, "Bad request: improperly terminated header.\n");
  80         return false;
  81     } else {
  82         /* Parse headers */
  83         char *p = buf;
  84         while (*p != ':') p++;
  85         p++;
  86
  87         while (p != end) {
  88             const char* key = p;
  89             while (*p) ++p;
  90             ++p;
  91             if (p == end) {
  92                 fprintf(stderr, "Bad request: key with no value.\n");
  93                 return false;
  94             }
  95
  96             char* val = p;
  97             while (*p) ++p;
  98             ++p;
  99
 100             if (strcmp(key, "QUERY_STRING") == 0) {
 101                 urldecode(val);
 102                 request_info->query_string_decoded = val;
 103             } else if (strcmp(key, "SCRIPT_PATH") == 0) {
 104                 request_info->script_path = val;
 105             } else if (strcmp(key, "PATH_INFO") == 0) {
 106                 request_info->path_info = val;
 107             } else if (strcmp(key, "SERVER_NAME") == 0) {
 108                 request_info->server_name = val;
 109             } else if (strcmp(key, "SERVER_PORT") == 0) {
 110                 request_info->server_port = val;
 111             } else if (strcmp(key, "REMOTE_ADDR") == 0) {
 112                 request_info->remote_addr = val;
 113             } else if (strcmp(key, "TLS_CLIENT_ISSUER") == 0) {
 114                 request_info->tls_client_issuer = val;
 115             } else if (strcmp(key, "TLS_CLIENT_ISSUER_CN") == 0) {
 116                 request_info->tls_client_issuer_cn = val;
 117             } else if (strcmp(key, "TLS_CLIENT_SUBJECT") == 0) {
 118                 request_info->tls_client_subject = val;
 119             } else if (strcmp(key, "TLS_CLIENT_SUBJECT_CN") == 0) {
 120                 request_info->tls_client_subject_cn = val;
 121             } else if (strcmp(key, "TLS_CLIENT_HASH") == 0) {
 122                 if (strncmp(val, "SHA256:", 7) == 0) val += 7;
 123                 request_info->tls_client_hash = val;
 124             }
 125         }
 126     }
 127
 128     return true;
 129 }
 130
 131 void runSCGI(const char *socket_path, respond_cb respond, void *respond_object)
 132 {
 133     // Unix socket gubbins based on
 134     // https://beej.us/guide/bgipc/html/multi/unixsock.html
 135
 136     const int s = socket(AF_UNIX, SOCK_STREAM, 0);
 137     if (s == -1) {
 138         perror("socket");
 139         exit(1);
 140     }
 141
 142     struct sockaddr_un local;
 143     local.sun_family = AF_UNIX;
 144     strcpy(local.sun_path, socket_path);
 145     unlink(local.sun_path);
 146     if (bind(s, (struct sockaddr *)&local,
 147                 strlen(local.sun_path) + sizeof(local.sun_family)) == -1) {
 148         perror("bind");
 149         exit(1);
 150     }
 151
 152     if (listen(s, 20) == -1) {
 153         perror("listen");
 154         exit(1);
 155     }
 156
 157     while (1) {
 158         const int s2 = accept(s, NULL, NULL);
 159         if (s2 == -1) {
 160             perror("accept");
 161             exit(1);
 162         }
 163
 164
 165         Request_Info request_info = { };
 166         if (parse_SCGI(s2, &request_info)) {
 167             respond(respond_object, &request_info, s2);
 168         }
 169     }
 170 }