Binary Data in JSON String. Something better than Base64

Question

The JSON format natively doesn\'t support binary data. The binary data has to be escaped so that it can be placed into a string element (i.e. zero or more Unicode chars in d

Answer 1

yEnc might work for you:

http://en.wikipedia.org/wiki/Yenc

"yEnc is a binary-to-text encoding scheme for transferring binary files in [text]. It reduces the overhead over previous US-ASCII-based encoding methods by using an 8-bit Extended ASCII encoding method. yEnc's overhead is often (if each byte value appears approximately with the same frequency on average) as little as 1–2%, compared to 33%–40% overhead for 6-bit encoding methods like uuencode and Base64. ... By 2003 yEnc became the de facto standard encoding system for binary files on Usenet."

However, yEnc is an 8-bit encoding, so storing it in a JSON string has the same problems as storing the original binary data — doing it the naïve way means about a 100% expansion, which is worse than base64.

Answer 2

Data type really concerns. I have tested different scenarios on sending the payload from a RESTful resource. For encoding I have used Base64(Apache) and for compression GZIP(java.utils.zip.*).The payload contains information about film,an image and an audio file. I have compressed and encoded the image and audio files which drastically degraded the performance. Encoding before compression turned out well. Image and audio content were sent as encoded and compressed bytes [] .

Answer 3

I ran into the same problem, and thought I'd share a solution: multipart/form-data.

By sending a multipart form you send first as string your JSON meta-data, and then separately send as raw binary (image(s), wavs, etc) indexed by the Content-Disposition name.

Here's a nice tutorial on how to do this in obj-c, and here is a blog article that explains how to partition the string data with the form boundary, and separate it from the binary data.

The only change you really need to do is on the server side; you will have to capture your meta-data which should reference the POST'ed binary data appropriately (by using a Content-Disposition boundary).

Granted it requires additional work on the server side, but if you are sending many images or large images, this is worth it. Combine this with gzip compression if you want.

IMHO sending base64 encoded data is a hack; the RFC multipart/form-data was created for issues such as this: sending binary data in combination with text or meta-data.