feat: redirect websites to open-source frontends

1. Adds code for redirecting annoying websites to their open-source
frontends, when these exist.

2. Organize this in a "plugins" folder

plugins/libre_redirect/libre_redirect.c

@@ -0,0 +1,69 @@
+#include "str_replace_start.h"
+#include <string.h>
+#include <stdio.h>
+#include <stdbool.h>
+#define LIBRE_N 19
+#define DEBUG false
+
+/* Inspired by https://libredirect.github.io/, but in C. */
+
+void str_init(char* str, int n){
+  for(int i=0; i<n; i++){
+    str[i] = ' ';
+  }
+  str[n] = '\0';
+} // could also use <https://manpages.ubuntu.com/manpages/impish/man3/strinit.3pub.html>
+
+int libre_redirect(const char* uri, char* output){
+  int l1 = strlen(uri);
+  int l2 = strlen(output);
+  
+  if((l2 - l1) < LIBRE_N){ 
+    if(DEBUG) printf("Not enough memory\n");
+    return 1; // not enough memory. 
+  }else{
+    char tmp_uri[l2++];
+    char tmp_output[l2++];
+    strcpy(tmp_uri, uri); // strcpy also copies the terminating '\0'
+    strcpy(tmp_output, output);
+  
+    char* annoying_sites[] = { 
+      "https://www.youtube.com", 
+      "https://www.reddit.com", 
+      "https://medium.com", 
+      "https://translate.google.com",
+      "https://forum.effectivealtruism.org",
+      "https://www.bloomberg.com",
+      "https://twitter.com"
+    };
+    char* alternatives[] = { 
+      "https://yt.artemislena.eu", 
+      "https://teddit.nunosempere.com", 
+      "https://scribe.rip", 
+      "https://simplytranslate.org/",
+      "https://ea.greaterwrong.com",
+      "https://archive.is/https://www.bloomberg.com",
+      "https://nitter.net"
+    };
+    int n = sizeof(annoying_sites)/sizeof(annoying_sites[0]);
+    for(int i=0; i<n ; i++){
+      int replace_check = str_replace_start(tmp_uri, annoying_sites[i], alternatives[i], output);
+      if(replace_check == 2){
+	if(DEBUG) printf("tmp_uri: %s\n", tmp_uri);
+	if(DEBUG) printf("output: %s\n", output);
+        // strcpy(output, tmp_uri);
+        // break;
+	return 2;
+      }else if(replace_check == 1){
+        if(DEBUG) printf("replace_check failed\n");
+        return 1;
+      }
+      strcpy(tmp_uri, output);
+      str_init(output, l2);
+    }
+    strcpy(output, tmp_uri);
+  }
+  if(DEBUG) printf("No match found\n\n");
+  return 0;
+  
+}

plugins/libre_redirect/libre_redirect.h

@@ -0,0 +1,9 @@
+#ifndef LIBRE_REDIRECT
+#define LIBRE_REDIRECT
+
+#define LIBRE_N 19
+
+int libre_redirect(const char* uri, char* uri_filtered);
+void str_init(char* str, int n);
+
+#endif

plugins/libre_redirect/str_replace_start.c

@@ -0,0 +1,60 @@
+#include <string.h>
+#include <stdbool.h>
+#include <stdio.h>
+#define DEBUG false
+
+/*
+See also: 
+* <https://web.archive.org/web/20160201212501/coding.debuntu.org/c-implementing-str_replace-replace-all-occurrences-substring>
+* https://github.com/irl/la-cucina/blob/master/str_replace.c
+*/
+
+int str_replace_start(const char* string, const char* target, const char* replacement, char* output){
+  
+  int l1 = strlen(string);
+  int l2 = strlen(target);
+  int l3 = strlen(replacement);
+  int l4 = strlen(output);
+  if(DEBUG) printf("%d,%d,%d,%d\n", l1, l2, l3, l4);
+  // if(DEBUG) printf("%s,%s,%s,%s\n", string, target, replacement, output);
+  
+  if((l4 < (l1 - l2 + l3)) || l4 < l1 ){
+    // Not enough memory in output string.
+    if(DEBUG) printf("String not long enough.\n");
+    return 1; 
+  } 
+  /* else if(l1 < l2){
+    // Not even possible that there is a match.
+    if(DEBUG) printf("Target larger than string.\n");
+    strcpy(output, string);
+  } */
+  else {
+    if(DEBUG) printf("Looking for a match for %s in %s.\n", target, string);
+    int match = true;
+    for(int i=0; i<l2; i++){
+      if(string[i] != target[i]){
+	match = false;
+	break;
+      }
+    }
+    if(match){
+      if(DEBUG) printf("Found match.\n");
+      for(int i=0; i<l3; i++){
+	output[i] = replacement[i];
+      }
+      int counter = l3;
+      for(int i=l2; i<l1; i++){
+        output[counter] = string[i];
+        counter++;
+      }
+      output[counter] = '\0';
+      return 2; // success
+    }
+    else {
+      if(DEBUG) printf("Did not find match.\n");
+      strcpy(output, string);
+    }
+  }
+
+  return 0;
+}

plugins/libre_redirect/str_replace_start.h

@@ -0,0 +1,6 @@
+#ifndef STR_REPLACE_H_
+#define STR_REPLACE_H_
+
+int str_replace_start(const char* string, const char* target, const char* replacement, char* output);
+
+#endif

plugins/libre_redirect/str_replace_test/build-example.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+CC=gcc
+
+FLAGS="-std=c99 -Wall -lm"
+
+SRC=example.c
+REQS="../str_replace_start.c ../libre_redirect.c"
+
+echo -e "\n\n\n"
+$CC $FLAGS $SRC $REQS -o example
+

plugins/libre_redirect/str_replace_test/example.c

@@ -0,0 +1,20 @@
+#include "../libre_redirect.h"
+#include <string.h>
+#include <stdio.h>
+
+int main(){
+  char uri[] = "https://reddit.com/r/blah";
+  
+  int l = LIBRE_N + strlen(uri) + 1;
+  char uri_filtered[l];
+  str_init(uri_filtered, l);
+
+  if(!libre_redirect(uri, uri_filtered)){
+    printf("Filtered uri: %s\n", uri_filtered);
+  }else{
+    printf("Uri: %s\n", uri);
+    // failure; do something with the original uri.
+  }
+}
+
+