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waaaaRapy/chunked.lua

Created September 23, 2016 21:47
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Toshiba FlashAir Lua -- send large binary response using chunked transfer
Raw
chunked.lua
print([[
HTTP/1.1 200 OK
Content-Type: image/jpeg
Transfer-Encoding: chunked
]])
IMG = "/img.jpg"
chunk_size = 8192
size = lfs.attributes(IMG).size
img = io.open(IMG)
repeat
size = size - chunk_size
if (size < 0) then
chunk_size = chunk_size + size
size = 0
end
print(string.format("%x", chunk_size))
print(img:read(chunk_size))
until size == 0
print("0")
print("")
img:close()
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waaaaRapy commented Sep 23, 2016 •
edited
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As of firmware version FA9CAW3AW3.00.01, io.stdout:write() seems to be not working (moreover, the card freeze when io.stdout:flush() is called and it can crush it's file system.) The other way to send response directly to a HTTP request is using print(), but it emits trailing \r\n so it can't send large binary data like embed jpeg preview image of raw image file in a row.

A solution for this problem is using chunked transfer encoding defined in HTTP/1.1. In this way, the response may be split into small chunks trailing with \r\n so you can use print() for sending these chunks.

Note: As far as you want to retrive a part of file, partial GET request from client side XMLHttpRequest with Range header would work.

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