curl: allow --header and --proxy-header read from file

So many headers can be provided as @filename.

Suggested-by: Timothe Litt

Closes curl#1486

docs/cmdline-opts/header.d

@@ -1,10 +1,9 @@
 Long: header
 Short: H
-Arg: <header>
-Help: Pass custom header LINE to server
+Arg: <header/@file>
+Help: Pass custom header(s) to server
 Protocols: HTTP
 ---
-
 Extra header to include in the request when sending HTTP to a server. You may
 specify any number of extra headers. Note that if you should add a custom
 header that has the same name as one of the internal ones curl would use, your
@@ -21,6 +20,10 @@ end-of-line marker, you should thus \fBnot\fP add that as a part of the header
 content: do not add newlines or carriage returns, they will only mess things up
 for you.
 
+Starting in 7.55.0, this option can take an argument in @filename style, which
+then adds a header for each line in the input file. Using @- will make curl
+read the header file from stdin.
+
 See also the --user-agent and --referer options.
 
 Starting in 7.37.0, you need --proxy-header to send custom headers intended

docs/cmdline-opts/proxy-header.d

@@ -1,6 +1,6 @@
 Long: proxy-header
-Arg: <header>
-Help: Pass custom header LINE to proxy
+Arg: <header/@file>
+Help: Pass custom header(s) to proxy
 Protocols: HTTP
 Added: 7.37.0
 ---
@@ -17,4 +17,8 @@ up for you.
 Headers specified with this option will not be included in requests that curl
 knows will not be sent to a proxy.
 
+Starting in 7.55.0, this option can take an argument in @filename style, which
+then adds a header for each line in the input file. Using @- will make curl
+read the header file from stdin.
+
 This option can be used multiple times to add/replace/remove multiple headers.

src/tool_getparam.c

@@ -1602,12 +1602,42 @@ ParameterError getparameter(const char *flag, /* f or -long-flag */
       break;
     case 'H':
       /* A custom header to append to a list */
-      if(subletter == 'p') /* --proxy-header */
-        err = add2list(&config->proxyheaders, nextarg);
-      else
-        err = add2list(&config->headers, nextarg);
-      if(err)
-        return err;
+      if(nextarg[0] == '@') {
+        /* read many headers from a file or stdin */
+        char *string;
+        size_t len;
+        bool use_stdin = !strcmp(&nextarg[1], "-");
+        FILE *file = use_stdin?stdin:fopen(&nextarg[1], FOPEN_READTEXT);
+        if(!file)
+          warnf(global, "Failed to open %s!\n", &nextarg[1]);
+        else {
+          if(PARAM_OK == file2memory(&string, &len, file)) {
+            /* Allow strtok() here since this isn't used threaded */
+            /* !checksrc! disable BANNEDFUNC 2 */
+            char *h = strtok(string, "\r\n");
+            while(h) {
+              if(subletter == 'p') /* --proxy-header */
+                err = add2list(&config->proxyheaders, h);
+              else
+                err = add2list(&config->headers, h);
+              if(err)
+                return err;
+              h = strtok(NULL, "\r\n");
+            }
+            free(string);
+          }
+          if(!use_stdin)
+            fclose(file);
+        }
+      }
+      else {
+        if(subletter == 'p') /* --proxy-header */
+          err = add2list(&config->proxyheaders, nextarg);
+        else
+          err = add2list(&config->headers, nextarg);
+        if(err)
+          return err;
+      }
       break;
     case 'i':
       config->include_headers = toggle; /* include the headers as well in the