Re: [LEDE-DEV] [PATCH] jshn: add functionality to read big JSON

[Arjen de Korte]

Citeren John Crispin <j...@phrozen.org>:

On 07/01/18 18:08, Christian Beier wrote:
The existing read functionality feeds the complete JSON to jshn as a
cmdline argument, leading to `-ash: jshn: Argument list too long`
errors for JSONs bigger than ca. 100KB.
This commit adds the ability to read the JSON directly from a file if
wanted, removing this shell-imposed size limit.

Tested on x86-64 and ar71xx. An mmap()-based solution was also evaluated,
but found to make no performance difference on either platform.

Signed-off-by: Christian Beier <dontm...@freeshell.org>

Hi Christian,

comment inline ...

---
 jshn.c     | 30 ++++++++++++++++++++++++++++--
 sh/jshn.sh |  4 ++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/jshn.c b/jshn.c
index 3188af5..eb72fb7 100644
--- a/jshn.c
+++ b/jshn.c
@@ -25,6 +25,8 @@
 #include <stdbool.h>
 #include <ctype.h>
 #include <getopt.h>
+#include <sys/stat.h>
+#include <fcntl.h>
 #include "list.h"
   #include "avl.h"
@@ -305,7 +307,7 @@ out:
   static int usage(const char *progname)
 {
-       fprintf(stderr, "Usage: %s [-n] [-i] -r <message>|-w\n", progname);
+	fprintf(stderr, "Usage: %s [-n] [-i] -r <message>|-R  
<file>|-w\n", progname);
        return 2;
 }
 @@ -338,6 +340,10 @@ int main(int argc, char **argv)
        struct env_var *vars;
        int i;
        int ch;
+       int fd;
+       struct stat sb;
+       char *fbuf;
+       int ret;
        avl_init(&env_vars, avl_strcmp_var, false, NULL);
        for (i = 0; environ[i]; i++);
@@ -359,7 +365,7 @@ int main(int argc, char **argv)
                avl_insert(&env_vars, &vars[i].avl);
        }
 -      while ((ch = getopt(argc, argv, "p:nir:w")) != -1) {
+       while ((ch = getopt(argc, argv, "p:nir:R:w")) != -1) {
                switch(ch) {
                case 'p':
                        var_prefix = optarg;
@@ -367,6 +373,26 @@ int main(int argc, char **argv)
                        break;
                case 'r':
                        return jshn_parse(optarg);
+               case 'R':
+                       if ((fd = open(optarg, O_RDONLY)) == -1) {
+                               fprintf(stderr, "Error opening %s\n", optarg);
+                               return 3;
+                       }
+                       if (fstat(fd, &sb) == -1) {
+                               fprintf(stderr, "Error getting size of %s\n", 
optarg);
+                               close(fd);
+                               return 3;
+                       }
+			if (!(fbuf = malloc(sb.st_size)) || read(fd, fbuf, sb.st_size)  
!= sb.st_size) {
+                               fprintf(stderr, "Error reading %s\n", optarg);
+                               free(fbuf);

this will blow up if the malloc fails.

How would it? If the malloc fails and returns a NULL pointer, the read  
will not be performed. Free'ing a NULL pointer is allowed, so although  
assigning a value in an if() statement is considered a no-no by some  
(including me), there is no reason for it to blow up.

please spli the if clause up into 2 blocks

Agreed (but for a different reason). A memory allocation error is  
different from failure to read from a file and error handlers should  
not treat them the same.

    John

+                               close(fd);
+                               return 3;
+                       }
+                       ret = jshn_parse(fbuf);
+                       free(fbuf);
+                       close(fd);
+                       return ret;
                case 'w':
                        return jshn_format(no_newline, indent);
                case 'n':
diff --git a/sh/jshn.sh b/sh/jshn.sh
index 1090814..66baccb 100644
--- a/sh/jshn.sh
+++ b/sh/jshn.sh
@@ -180,6 +180,10 @@ json_load() {
        eval "`jshn -r "$1"`"
 }
 +json_load_file() {
+       eval "`jshn -R "$1"`"
+}
+
 json_dump() {
        jshn "$@" ${JSON_PREFIX:+-p "$JSON_PREFIX"} -w
 }


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