When debugging network applications it's common to look at the data being sent to and from the application, using tools like e.g., tcpdump or wireshark.
When that data is sent over TLS, it's often times harder to use these tools due to the private keys for the TLS sessions not being available to the person doing the debugging.
A commonly used library for sending data over TLS is OpenSSL.
openssl-hook uses LD_PRELOAD to hook the OpenSSL functions SSL_read and SSL_write and writes the read/written data to disk for later inspection. This can be used to debug network applications sending/receiving data using a dynamically linked OpenSSL library.
The logged data is written to hooklog.bin in the current working directory. The file format is platform-dependent.
Any encountered errors in the hook code gets written to stderr. Hook errors causes application termination.
using a POSIX shell and socat:
$ make
cc -Wall -Werror -g -fPIC -shared -o hook.so.1 hook.c -lc
cc -Wall -Werror -g -o print-hooklog print-hooklog.c -lc
$ printf 'GET / HTTP/1.1\r\nHost: www.google.com\r\n\r\n' | \
LD_PRELOAD=`pwd`/hook.so.1 \
socat stdio openssl-connect:www.google.com:443
[...]
$ ./print-hooklog hooklog.bin
write - 192.168.0.8 39808 -> 83.255.235.89 443
00000000 47 45 54 20 2f 20 48 54 54 50 2f 31 2e 31 0d 0a |GET / HTTP/1.1..|
00000010 48 6f 73 74 3a 20 77 77 77 2e 67 6f 6f 67 6c 65 |Host: www.google|
00000020 2e 63 6f 6d 0d 0a 0d 0a |.com....|
00000028
read - 83.255.235.89 443 -> 192.168.0.8 39808
00000000 48 54 54 50 2f 31 2e 31 20 33 30 32 20 46 6f 75 |HTTP/1.1 302 Fou|
00000010 6e 64 0d 0a 43 61 63 68 65 2d 43 6f 6e 74 72 6f |nd..Cache-Contro|
00000020 6c 3a 20 70 72 69 76 61 74 65 0d 0a 43 6f 6e 74 |l: private..Cont|
00000030 65 6e 74 2d 54 79 70 65 3a 20 74 65 78 74 2f 68 |ent-Type: text/h|
00000040 74 6d 6c 3b 20 63 68 61 72 73 65 74 3d 55 54 46 |tml; charset=UTF|
00000050 2d 38 0d 0a 4c 6f 63 61 74 69 6f 6e 3a 20 68 74 |-8..Location: ht|
00000060 74 70 73 3a 2f 2f 77 77 77 2e 67 6f 6f 67 6c 65 |tps://www.google|
00000070 2e 73 65 2f 3f 67 66 65 5f 72 64 3d 63 72 26 65 |.se/?gfe_rd=cr&e|
00000080 69 3d 64 4b 71 51 56 70 47 67 47 49 71 41 38 51 |i=dKqQVpGgGIqA8Q|
00000090 66 6c 6c 71 61 41 42 51 0d 0a 43 6f 6e 74 65 6e |fllqaABQ..Conten|
000000a0 74 2d 4c 65 6e 67 74 68 3a 20 32 35 39 0d 0a 44 |t-Length: 259..D|
000000b0 61 74 65 3a 20 53 61 74 2c 20 30 39 20 4a 61 6e |ate: Sat, 09 Jan|
000000c0 20 32 30 31 36 20 30 36 3a 33 36 3a 33 36 20 47 | 2016 06:36:36 G|
000000d0 4d 54 0d 0a 53 65 72 76 65 72 3a 20 47 46 45 2f |MT..Server: GFE/|
000000e0 32 2e 30 0d 0a 0d 0a 3c 48 54 4d 4c 3e 3c 48 45 |2.0....<HTML><HE|
000000f0 41 44 3e 3c 6d 65 74 61 20 68 74 74 70 2d 65 71 |AD><meta http-eq|
00000100 75 69 76 3d 22 63 6f 6e 74 65 6e 74 2d 74 79 70 |uiv="content-typ|
00000110 65 22 20 63 6f 6e 74 65 6e 74 3d 22 74 65 78 74 |e" content="text|
00000120 2f 68 74 6d 6c 3b 63 68 61 72 73 65 74 3d 75 74 |/html;charset=ut|
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00000170 68 65 20 64 6f 63 75 6d 65 6e 74 20 68 61 73 20 |he document has |
00000180 6d 6f 76 65 64 0a 3c 41 20 48 52 45 46 3d 22 68 |moved.<A HREF="h|
00000190 74 74 70 73 3a 2f 2f 77 77 77 2e 67 6f 6f 67 6c |ttps://www.googl|
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