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POPython: subprocess.stdin.write is not working properly
 

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  1. POPython: subprocess.stdin.write is not working properly
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    <p>I'm new to python but I can code and debug a bit. The following problem has been on my head for the past couple of days and looking out for an answer. Any help is much appreciated. Task: I wanted to do an interactive telnet (I know there is an telnet library, but we are not using it for various reasons). For this purpose, I use a subprocess.popen</p> <pre><code>p = subprocess.Popen(telnet_command, stdin = subprocess.PIPE, stdout = outputfileobj, stderr = errorfileobj) </code></pre> <p>I do a poll() to see if the server has got connected to the session. Once I verified, I proceed to write to the stdin for interactive communication.</p> <pre><code>inputTxt = 'GET / HTTP/1.1\nHost: ' + hostheader + '\n\n' p.stdin.write(inputTxt) p.stdin.flush() </code></pre> <p>Here is where the problem has occurred. I get the http response (or atleast output) for 5/6 times but 1/6 time, I do not get a output and the subprocess gets terminated - which is not possible.</p> <p>I ran a system trace for the failure case and please find below the same.</p> <pre><code>16129 write(7, "GET / HTTP/1.1\nHost: www.google."..., 37) = 37 16129 gettimeofday({1310538497, 134474}, NULL) = 0 16129 futex(0x81993a8, FUTEX_WAKE, 1) = 0 16129 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=56, ...}) = 0 16129 fstat64(4, {st_mode=S_IFREG|0644, st_size=520689, ...}) = 0 16129 _llseek(4, 520689, [520689], SEEK_SET) = 0 16129 stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=56, ...}) = 0 16129 write(4, "2011-07-13 06:28:17,134 : pconns"..., 170) = 170 16129 futex(0x81d3b30, FUTEX_WAKE, 1) = 0 16129 waitpid(16198, 0xffa945e8, WNOHANG) = 0 16129 gettimeofday({1310538497, 135160}, NULL) = 0 16129 fstat64(6, {st_mode=S_IFREG|0644, st_size=81, ...}) = 0 16129 fstat64(6, {st_mode=S_IFREG|0644, st_size=81, ...}) = 0 16129 mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xf74b9000 16129 _llseek(6, 0, [0], SEEK_SET) = 0 16129 fstat64(6, {st_mode=S_IFREG|0644, st_size=81, ...}) = 0 16129 _llseek(6, 0, [0], SEEK_CUR) = 0 16129 read(6, "Trying 74.125.236.48...\nConnecte"..., 4096) = 81 16129 read(6, "", 4096) = 0 16129 close(6) = 0 16129 munmap(0xf74b9000, 4096) = 0 16129 gettimeofday({1310538497, 135778}, NULL) = 0 16129 futex(0x81993a8, FUTEX_WAKE, 1) = 0 16198 &lt;... select resumed&gt; ) = 1 (in [0]) 16198 read(0, "GET / HTTP/1.1\nHost: www.google."..., 8191) = 37 16129 stat64("/etc/localtime", &lt;unfinished ...&gt; 16198 ioctl(1, TCFLSH, 0) = -1 ENOTTY (Inappropriate ioctl for device) 16129 &lt;... stat64 resumed&gt; {st_mode=S_IFREG|0644, st_size=56, ...}) = 0 16198 select(4, [0 3], [3], [3], {0, 0}) = 1 (out [3], left {0, 0}) 16129 fstat64(4, {st_mode=S_IFREG|0644, st_size=520859, ...}) = 0 16198 send(3, "GET / HTTP/1.1\r\nHos\377\363\377\375\6", 24, 0 &lt;unfinished ...&gt; 16129 _llseek(4, 520859, &lt;unfinished ...&gt; 16198 &lt;... send resumed&gt; ) = 24 16198 select(4, [0 3], [3], [3], {0, 0} &lt;unfinished ...&gt; 16129 &lt;... _llseek resumed&gt; [520859], SEEK_SET) = 0 16198 &lt;... select resumed&gt; ) = 1 (out [3], left {0, 0}) 16198 send(3, ": www.google.com\r\n\r\n", 20, 0 &lt;unfinished ...&gt; 16129 stat64("/etc/localtime", &lt;unfinished ...&gt; 16198 &lt;... send resumed&gt; ) = 20 </code></pre> <p>If you closely look at the line <b>16198 send(3, "GET / HTTP/1.1\r\nHos\377\363\377\375\6", 24, 0 </b> in the trace, the string "Hos<b>t</b>" is replaced by some "Hos<b>\377\363\377\375\6</b>". I'm not sure why this occurs once in a while and also this closes the telnet connection I established. Please let me know if you need more data.</p>
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      1. POPython: subprocess.stdin.write is not working properly
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      1. POPython: subprocess.stdin.write is not working properly
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    1. COWhy are you making HTTP request to a telnet server?, or you are just testing connecting to google.com at 80?
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      1. UScyraxjoe
    2. COWe are trying to check if a server support persistant connections(can post multiple requests after getting connected).
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      1. POPython: subprocess.stdin.write is not working properly
      1. USVelu Sankaran
 

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