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

[John Crispin]

On 17/01/18 10:44, Arjen de Korte wrote:
> Citeren John Crispin <john at 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 <dontmind at 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.

ok, point taken ....

>
>> 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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>
>
>
>
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