Doesn't handle Expect: 100-Continue

[therc]

When e.g. curl sends a request with content length greater than 1024, it also sends an Expect: 100-Continue header.

aws-es-proxy returns the 100 header, but probably does not pass it along to ES, causing a mismatch. Sample trace:

=> Send header, 201 bytes (0xc9)
0000: 50 55 54 20 2f 5f 74 65 6d 70 6c 61 74 65 2f 6b PUT /_template/k
[...]
0040: 30 30 0d 0a 55 73 65 72 2d 41 67 65 6e 74 3a 20 00..User-Agent: 
0050: 63 75 72 6c 2f 37 2e 34 33 2e 30 0d 0a 41 63 63 curl/7.43.0..Acc
0060: 65 70 74 3a 20 2a 2f 2a 0d 0a 43 6f 6e 74 65 6e ept: */*..Conten
0070: 74 2d 4c 65 6e 67 74 68 3a 20 31 31 33 34 0d 0a t-Length: 1134..
0080: 43 6f 6e 74 65 6e 74 2d 54 79 70 65 3a 20 61 70 Content-Type: ap
0090: 70 6c 69 63 61 74 69 6f 6e 2f 78 2d 77 77 77 2d plication/x-www-
00a0: 66 6f 72 6d 2d 75 72 6c 65 6e 63 6f 64 65 64 0d form-urlencoded.
00b0: 0a 45 78 70 65 63 74 3a 20 31 30 30 2d 63 6f 6e .Expect: 100-con
00c0: 74 69 6e 75 65 0d 0a 0d 0a                      tinue....
<= Recv header, 23 bytes (0x17)
0000: 48 54 54 50 2f 31 2e 31 20 31 30 30 20 43 6f 6e HTTP/1.1 100 Con
0010: 74 69 6e 75 65 0d 0a                            tinue..
=> Send data, 1134 bytes (0x46e)
0000: 7b 20 20 22 74 65 6d 70 6c 61 74 65 22 3a 20 22 {  "template": "

Error:

The Canonical String for this request should have been
'PUT
/_template/k[...]

accept:*/*
content-length:1134
content-type:application/x-www-form-urlencoded
expect:
host:[...]
[...]