7.76.1 outputs invalid JSON in `--write-out %{json}` (a few versions back it was still fine)

[michalrus]

I did this

$ curl --write-out '%{json}' https://google.com/ --output /dev/null --silent 

{"content_type":"text/html; charset=UTF-8","errormsg":null,"exitcode":0,"filename_effective":"/dev/null","ftp_entry_path":null,"http_code":301,"http_connect":000,"http_version":"2","local_ip":"10.0.2.100","local_port":45384,"method":"GET","num_connects":1,"num_headers":12,"num_redirects":0,"proxy_ssl_verify_result":0,"redirect_url":"https://www.google.com/","referer":null,"remote_ip":"142.250.185.206","remote_port":443,"response_code":301,"scheme":"HTTPS","size_download":220,"size_header":639,"size_request":72,"size_upload":0,"speed_download":1057,"speed_upload":0,"ssl_verify_result":0,"time_appconnect":0.133558,"time_connect":0.046523,"time_namelookup":0.005388,"time_pretransfer":0.133639,"time_redirect":0.000000,"time_starttransfer":0.206770,"time_total":0.208079,"url":"https://google.com/","url_effective":"https://google.com/","urlnum":0,"curl_version":"libcurl/7.76.1 OpenSSL/1.1.1j zlib/1.2.11 brotli/1.0.9 nghttp2/1.42.0"}

Notice this part:

"http_connect":000

This is not valid JSON, and it breaks different parsers:

• e.g. Python’s stdlib json.loads(),
• or https://jsonformatter.curiousconcept.com/
• or https://jsonlint.com/

Error: Parse error on line 8:
...1,	"http_connect": 000,	"http_version"
----------------------^
Expecting 'STRING', 'NUMBER', 'NULL', 'TRUE', 'FALSE', '{', '[', got 'undefined'

Perhaps you could add a unit test to verify said JSON validity with some external tool?

I expected the following

Valid JSON.

curl/libcurl version

curl 7.76.1 (x86_64-alpine-linux-musl) libcurl/7.76.1 OpenSSL/1.1.1j zlib/1.2.11 brotli/1.0.9 nghttp2/1.42.0
Release-Date: 2021-04-14
Protocols: dict file ftp ftps gopher gophers http https imap imaps mqtt pop3 pop3s rtsp smb smbs smtp smtps telnet tftp 
Features: alt-svc AsynchDNS brotli HTTP2 HTTPS-proxy IPv6 Largefile libz NTLM NTLM_WB SSL TLS-SRP UnixSockets

operating system

alpine:3.13.2 on:

Linux 1df3df7de41f 5.10.23 #1-NixOS SMP Thu Mar 11 13:17:30 UTC 2021 x86_64 Linux

[jay]

curl/src/tool_writeout.c

Lines 260 to 272 in 566b74a

	if(valid) {
	if(use_json)
	fprintf(stream, "\"%s\":", wovar->name);
	if(wovar->id == VAR_HTTP_CODE || wovar->id == VAR_HTTP_CODE_PROXY)
	fprintf(stream, "%03ld", longinfo);
	else
	fprintf(stream, "%ld", longinfo);
	}
	else {
	if(use_json)
	fprintf(stream, "\"%s\":null", wovar->name);
	}

I think I was trying to imitate the existing non-json --write-out for the http codes.

diff --git a/src/tool_writeout.c b/src/tool_writeout.c
index 5296778..ed7a341 100644
--- a/src/tool_writeout.c
+++ b/src/tool_writeout.c
@@ -259,12 +259,13 @@ static int writeLong(FILE *stream, const struct writeoutvar *wovar,
 
   if(valid) {
     if(use_json)
-      fprintf(stream, "\"%s\":", wovar->name);
-
-    if(wovar->id == VAR_HTTP_CODE || wovar->id == VAR_HTTP_CODE_PROXY)
-      fprintf(stream, "%03ld", longinfo);
-    else
-      fprintf(stream, "%ld", longinfo);
+      fprintf(stream, "\"%s\":%ld", wovar->name, longinfo);
+    else {
+      if(wovar->id == VAR_HTTP_CODE || wovar->id == VAR_HTTP_CODE_PROXY)
+        fprintf(stream, "%03ld", longinfo);
+      else
+        fprintf(stream, "%ld", longinfo);
+    }
   }
   else {
     if(use_json)

[bagder]

Is the problem that the number is zero-prefixed? BTW, 'jq' parses this fine...

[bagder]

(sorry, wrong button)

[jay]

Is the problem that the number is zero-prefixed?

seems so

[bagder]

@jay the new test 972 in #6906 seems to work so I pushed your proposed commit from here in that PR as well, as it worked fine locally for me with the new test.

[gvanem]

Is the problem that the number is zero-prefixed?

seems so

Yes. Testing using jsondump from https://github.com/zserge/jsmn:

c:\> curl -k --write-out "%%{json}" https://google.com/ --output NUL -s | jsondump - --verify
{
  "content_type": "text/html; charset=UTF-8",
  "errormsg": null,
  "exitcode": 0,
  "filename_effective": "NUL",
  "ftp_entry_path": null,
  "http_code": 301,
  "http_connect": line 1, col 153: [code=8] unexpected char

[michalrus]

@bagder @jay I encountered the same issue with 2 more fields:

$ curl --write-out '%{json}' http://i-dont-exist.xxx
curl: (6) Could not resolve host: i-dont-exist.xxx

{"content_type":null,"errormsg":"Could not resolve host: i-dont-exist.xxx","exitcode":6,"filename_effective":null,"ftp_entry_path":null,"http_code":000,"http_connect":000,"http_version":"0","local_ip":"","local_port":0,"method":"GET","num_connects":0,"num_headers":0,"num_redirects":0,"proxy_ssl_verify_result":0,"redirect_url":null,"referer":null,"remote_ip":"","remote_port":0,"response_code":000,"scheme":null,"size_download":0,"size_header":0,"size_request":0,"size_upload":0,"speed_download":0,"speed_upload":0,"ssl_verify_result":0,"time_appconnect":0.000000,"time_connect":0.000000,"time_namelookup":0.000000,"time_pretransfer":0.000000,"time_redirect":0.000000,"time_starttransfer":0.000000,"time_total":0.004487,"url":"http://i-dont-exist.xxx","url_effective":"http://i-dont-exist.xxx/","urlnum":0,"curl_version":"libcurl/7.76.1 OpenSSL/1.1.1j zlib/1.2.11 brotli/1.0.9 nghttp2/1.42.0"}

• "http_connect":000
• "response_code":000
• "http_code":000

Looking at the diff of the fix, I think they should be covered as well, but asking just to make sure.

Thank you for a quick fix!