libcurl Notes
Table of Contents
libcurl Overview
- homepage: http://curl.haxx.se/libcurl/
- example: http://curl.haxx.se/libcurl/c/example.html
Examples
download quandl csv
#include <stdio.h> #include <curl/curl.h> #include <string> size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) { size_t written = fwrite(ptr, size, nmemb, stream); return written; } int main(void) { CURL *curl; FILE *fp; CURLcode res; const char *url = "https://www.quandl.com/api/v3/datasets/WIKI/FB.csv"; char outfilename[FILENAME_MAX] = "fb.csv"; curl = curl_easy_init(); if (curl) { fp = fopen(outfilename,"wb"); curl_easy_setopt(curl, CURLOPT_URL, url); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data); curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp); res = curl_easy_perform(curl); /* always cleanup */ curl_easy_cleanup(curl); fclose(fp); } return 0; }
download yahoo csv
#include <stdio.h> #include <curl/curl.h> #include <string> size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) { size_t written = fwrite(ptr, size, nmemb, stream); return written; } int main(void) { CURL *curl; FILE *fp; CURLcode res; const char *url = "http://finance.yahoo.com/d/quotes.csv?s=XOM+BBDb.TO+JNJ+MSFT&f=snd1l1yr"; char outfilename[FILENAME_MAX] = "quotes.csv"; curl = curl_easy_init(); if (curl) { fp = fopen(outfilename,"wb"); curl_easy_setopt(curl, CURLOPT_URL, url); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data); curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp); curl_easy_setopt(curl, CURLOPT_NOBODY, 0L); curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L); res = curl_easy_perform(curl); /* always cleanup */ curl_easy_cleanup(curl); fclose(fp); } return 0; }
Debug1
static void dump(const char *text, FILE *stream, unsigned char *ptr, size_t size) { size_t i; size_t c; unsigned int width=0x10; fprintf(stream, "%s, %10.10ld bytes (0x%8.8lx)\n", text, (long)size, (long)size); for(i=0; i<size; i+= width) { fprintf(stream, "%4.4lx: ", (long)i); /* show hex to the left */ for(c = 0; c < width; c++) { if(i+c < size) fprintf(stream, "%02x ", ptr[i+c]); else fputs(" ", stream); } /* show data on the right */ for(c = 0; (c < width) && (i+c < size); c++) fputc((ptr[i+c]>=0x20) && (ptr[i+c]<0x80)? ptr[i+c]:'.', stream); fputc('\n', stream); /* newline */ } } static int my_trace(CURL *handle, curl_infotype type, char *data, size_t size, void *userp) { const char *text; (void)handle; /* prevent compiler warning */ switch (type) { case CURLINFO_TEXT: fprintf(stderr, "== Info: %s", data); default: /* in case a new one is introduced to shock us */ return 0; case CURLINFO_HEADER_OUT: text = "=> Send header"; break; case CURLINFO_DATA_OUT: text = "=> Send data"; break; case CURLINFO_SSL_DATA_OUT: text = "=> Send SSL data"; break; case CURLINFO_HEADER_IN: text = "<= Recv header"; break; case CURLINFO_DATA_IN: text = "<= Recv data"; break; case CURLINFO_SSL_DATA_IN: text = "<= Recv SSL data"; break; } dump(text, stderr, (unsigned char *)data, size); return 0; } curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, my_trace); curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
Issues
SSL issues
$ curl https://www.google.com curl: (60) SSL certificate problem: unable to get local issuer certificate More details here: http://curl.haxx.se/docs/sslcerts.html curl performs SSL certificate verification by default, using a "bundle" of Certificate Authority (CA) public keys (CA certs). If the default bundle file isn't adequate, you can specify an alternate file using the --cacert option. If this HTTPS server uses a certificate signed by a CA represented in the bundle, the certificate verification probably failed due to a problem with the certificate (it might be expired, or the name might not match the domain name in the URL). If you'd like to turn off curl's verification of the certificate, use the -k (or --insecure) option.
- Check curl support
$ curl -V curl 7.46.0 (Linux) libcurl/7.46.0 OpenSSL/1.0.1 zlib/1.2.3.4 Protocols: dict file ftp ftps gopher http https imap imaps pop3 pop3s rtsp smb smbs smtp smtps telnet tftp Features: IPv6 NTLM SSL libz UnixSockets
- Check curl ca bundle install path
$ curl-config --ca
It is empty.
- Reinstall curl and check ca bundle path
$ curl-config --ca /etc/ssl/certs/ca-certificates.crt
More, curl use env(.curlrc):
capath=/etc/ssl/certs/ CURL_CA_BUNDLE=/etc/ssl/certs/ca-certificates.crt