Base64 decoding error, when posting an encoded image to an API

Getting Started Newbie Questions
#1

Hello,

I am trying to POST a local image (photo2.jpg) to Google Vision API, but I am stuck with error message:

Invalid value at 'requests[0].image.content' (TYPE\_BYTES), Base64 decoding failed for \"..base64\""

The code is:

 -- loading the binary file local path2 = system.pathForFile( "photo2.jpg", system.DocumentsDirectory ) local file2 = io.open(path2,"rb") local temp = file2:read("\*a") io.close(file2) file2 = nil -- converting the binary stored in temp to base64 local function base64encode(data) local len = data:len() local t = {} for i=1,len,384 do local n = math.min(384, len+1-i) if n \> 0 then local s = data:sub(i, i+n-1) local enc, \_ = mime.b64(s) t[#t+1] = enc end end return table.concat(t) end local base64 = base64encode(temp) local function networkListener( event ) local res = json.prettify( event.response ) local decoded = json.decode( res ) if ( event.isError ) then print( "Network error: ", event.response ) else print( "Result: " .. ( res ) ) --This seems to display Base64 properly print(base64) end end --Somehow Base64 decoding failed! local headers = {} headers["Content-Type"] = "application/json" local body = '{"requests": [{"image": {"content": "..base64"},"features": [{"type": "TEXT\_DETECTION"}]}]}' local params = {} params.headers = headers params.body = body network.request( "https://vision.googleapis.com/v1/images:annotate?key="..apikey, "POST", networkListener, params )

I also tried the following simpler function (in place of base64encode function above):

local mime = require("mime") local result = mime.b64(temp)

It returns the same error.

In both cases, the Corona Simulator console seems to output Base64 data properly…

I look at documentation of the Google API and check Base64 related websites, but run out of ideas how to solve this. Do you have similar experience? Any hint?

#2

Looks like you need to specify the body using Lua table like this:

[lua]

local body = {
   requests = {
      image = {
         content = “…”,
         features = {
            type = “TEXT_DETECTION”,
         },
      },
   },
}

[/lua]

#3

sort out the string delimiters and concatenation in the assignment to “body” - you’re passing literally “…base64”, not its value

#4

Thank you for quick help! @Dave Yang and @davebollinger

So, it was quite simple. I was not entirely sure how to insert a variable in Lua. After a few trials, only 1 line of code change works:

    local body = '{"requests": [{"image": {"content": "'..base64..'"},"features": [{"type": "TEXT\_DETECTION"}]}]}'

If I understand correctly (https://docs.coronalabs.com/api/library/network/request.html), body has to be string. So, my syntax works fine. Table should be used when it specifies a file as the content of the body.

Nevertheless, it was good to ask, as I am not sure if I could find a solution by myself. Cheers!

#5

Looks like you need to specify the body using Lua table like this:

[lua]

local body = {
   requests = {
      image = {
         content = “…”,
         features = {
            type = “TEXT_DETECTION”,
         },
      },
   },
}

[/lua]

#6

sort out the string delimiters and concatenation in the assignment to “body” - you’re passing literally “…base64”, not its value

#7

Thank you for quick help! @Dave Yang and @davebollinger

So, it was quite simple. I was not entirely sure how to insert a variable in Lua. After a few trials, only 1 line of code change works:

    local body = '{"requests": [{"image": {"content": "'..base64..'"},"features": [{"type": "TEXT\_DETECTION"}]}]}'

If I understand correctly (https://docs.coronalabs.com/api/library/network/request.html), body has to be string. So, my syntax works fine. Table should be used when it specifies a file as the content of the body.

Nevertheless, it was good to ask, as I am not sure if I could find a solution by myself. Cheers!