var: add a '64dec' function that can base64 decode a string

Verified in test 455 and 487.

If the provided string cannot be base64-decoded, it will instead use
"[64dec-fail]" (without the quotes).

Documented

Ref: curl#16288
Closes curl#16330

docs/cmdline-opts/_VARIABLES.md

@@ -27,10 +27,10 @@ set:
 When expanding variables, curl supports a set of functions that can make the
 variable contents more convenient to use. It can trim leading and trailing
 white space with `trim`, it can output the contents as a JSON quoted string
-with `json`, URL encode the string with `url` or base64 encode it with `b64`.
-To apply functions to a variable expansion, add them colon separated to the
-right side of the variable. Variable content holding null bytes that are not
-encoded when expanded cause error.
+with `json`, URL encode the string with `url`, base64 encode it with `b64` and
+base64 decode it with `64dec`. To apply functions to a variable expansion, add
+them colon separated to the right side of the variable. Variable content
+holding null bytes that are not encoded when expanded cause error.
 
 Example: get the contents of a file called $HOME/.secret into a variable
 called "fix". Make sure that the content is trimmed and percent-encoded when

docs/cmdline-opts/variable.md

@@ -66,30 +66,45 @@ error.
 
 Available functions:
 
-## trim
+## `trim`
+
 removes all leading and trailing white space.
 
 Example:
 
     curl --expand-url https://example.com/{{var:trim}}
 
-## json
+## `json`
+
 outputs the content using JSON string quoting rules.
 
 Example:
 
     curl --expand-data {{data:json}} https://example.com
 
-## url
+## `url`
+
 shows the content URL (percent) encoded.
 
 Example:
 
     curl --expand-url https://example.com/{{path:url}}
 
-## b64
+## `b64`
+
 expands the variable base64 encoded
 
 Example:
 
     curl --expand-url https://example.com/{{var:b64}}
+
+## `64dec`
+
+decodes a base64 encoded character sequence. If the sequence is not possible
+to decode, it instead outputs `[64dec-fail]`
+
+Example:
+
+    curl --expand-url https://example.com/{{var:64dec}}
+
+(Added in 8.13.0)

src/var.c

@@ -91,6 +91,8 @@ static const struct tool_var *varcontent(struct GlobalConfig *global,
 #define FUNC_URL_LEN (sizeof(FUNC_URL) - 1)
 #define FUNC_B64 "b64"
 #define FUNC_B64_LEN (sizeof(FUNC_B64) - 1)
+#define FUNC_64DEC "64dec" /* base64 decode */
+#define FUNC_64DEC_LEN (sizeof(FUNC_64DEC) - 1)
 
 static ParameterError varfunc(struct GlobalConfig *global,
                               char *c, /* content */
@@ -179,6 +181,27 @@ static ParameterError varfunc(struct GlobalConfig *global,
           break;
       }
     }
+    else if(FUNCMATCH(f, FUNC_64DEC, FUNC_64DEC_LEN)) {
+      f += FUNC_64DEC_LEN;
+      curlx_dyn_reset(out);
+      if(clen) {
+        unsigned char *enc;
+        size_t elen;
+        CURLcode result = curlx_base64_decode(c, &enc, &elen);
+        /* put it in the output */
+        if(result) {
+          if(curlx_dyn_add(out, "[64dec-fail]"))
+            err = PARAM_NO_MEM;
+        }
+        else {
+          if(curlx_dyn_addn(out, enc, elen))
+            err = PARAM_NO_MEM;
+          curl_free(enc);
+        }
+        if(err)
+          break;
+      }
+    }
     else {
       /* unsupported function */
       errorf(global, "unknown variable function in '%.*s'",

tests/data/Makefile.am

@@ -78,7 +78,7 @@ test444 test445 test446 test447 test448 test449 test450 test451 test452 \
 test453 test454 test455 test456 test457 test458 test459 test460 test461 \
 test462 test463 test467 test468 test469 test470 test471 test472 test473 \
 test474 test475 test476 test477 test478 test479 test480 test481 test482 \
-test483 test484 test485 test486 \
+test483 test484 test485 test486 test487 \
 test490 test491 test492 test493 test494 test495 test496 test497 test498 \
 test499 test500 test501 test502 test503 test504 test505 test506 test507 \
 test508 test509 test510 test511 test512 test513 test514 test515 test516 \

tests/data/test455

@@ -34,15 +34,15 @@ http
 Variable using base64
 </name>
 <command>
---variable moby="Call me Ishmael" --expand-url "http://%HOSTIP:%HTTPPORT/{{moby:b64}}/%TESTNUMBER"
+--variable moby="Call me Ishmael" --variable what=%b64[white-whale]b64% --expand-url "http://%HOSTIP:%HTTPPORT/{{moby:b64}}/{{what:64dec}}/%TESTNUMBER"
 </command>
 </client>
 
 #
 # Verify data after the test has been "shot"
 <verify>
 <protocol crlf="yes">
-GET /%b64[Call me Ishmael]b64%/%TESTNUMBER HTTP/1.1
+GET /%b64[Call me Ishmael]b64%/white-whale/%TESTNUMBER HTTP/1.1
 Host: %HOSTIP:%HTTPPORT
 User-Agent: curl/%VERSION
 Accept: */*

tests/data/test487

@@ -0,0 +1,52 @@
+<testcase>
+<info>
+<keywords>
+variables
+</keywords>
+</info>
+
+#
+# Server-side
+<reply>
+<data crlf="yes">
+HTTP/1.1 200 OK
+Date: Tue, 09 Nov 2010 14:49:00 GMT
+Server: test-server/fake
+Last-Modified: Tue, 13 Jun 2000 12:10:00 GMT
+ETag: "21025-dc7-39462498"
+Accept-Ranges: bytes
+Content-Length: 6
+Connection: close
+Content-Type: text/html
+Funny-head: yesyes
+
+-foo-
+</data>
+</reply>
+
+#
+# Client-side
+<client>
+<server>
+http
+</server>
+<name>
+Variable using 64dec with bad base64
+</name>
+<command>
+--variable what=not-base64-data --expand-url "http://%HOSTIP:%HTTPPORT/{{what:64dec}}/%TESTNUMBER" -g
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+<protocol crlf="yes">
+GET /[64dec-fail]/%TESTNUMBER HTTP/1.1
+Host: %HOSTIP:%HTTPPORT
+User-Agent: curl/%VERSION
+Accept: */*
+
+</protocol>
+</verify>
+</testcase>