init: Allow basic environment variable expansion in env assignment

Allow environment variable expansion in 'export' command if the
value begins with "${_var_}" (where "${_var_}" will be replaced
with the current value of environment variable _var_).  Expansion
will only occur one time.

e.g.
export BOOTCLASSPATH ${BOOTCLASSPATH}:/system/framework/abc.jar
(cherry picked from commit 7940299507f15055851a6e8b61ae8d8a7d7f3484)

Change-Id: If9e4adfa1aba2c7a4ca243978ced3c46c2cb4d73

init/init.c

@@ -105,21 +105,105 @@ static unsigned emmc_boot = 0;
 
 static unsigned charging_mode = 0;
 
+static const char *expand_environment(const char *val)
+{
+    int n;
+    const char *prev_pos = NULL, *copy_pos;
+    size_t len, prev_len = 0, copy_len;
+    char *expanded;
+
+    /* Basic expansion of environment variable; for now
+       we only assume 1 expansion at the start of val
+       and that it is marked as ${var} */
+    if (!val) {
+        return NULL;
+    }
+
+    if ((val[0] == '$') && (val[1] == '{')) {
+        for (n = 0; n < 31; n++) {
+            if (ENV[n]) {
+                len = strcspn(ENV[n], "=");
+                if (!strncmp(&val[2], ENV[n], len)
+                      && (val[2 + len] == '}')) {
+                    /* Matched existing env */
+                    prev_pos = &ENV[n][len + 1];
+                    prev_len = strlen(prev_pos);
+                    break;
+                }
+            }
+        }
+        copy_pos = index(val, '}');
+        if (copy_pos) {
+            copy_pos++;
+            copy_len = strlen(copy_pos);
+        } else {
+            copy_pos = val;
+            copy_len = strlen(val);
+        }
+    } else {
+        copy_pos = val;
+        copy_len = strlen(val);
+    }
+
+    len = prev_len + copy_len + 1;
+    expanded = malloc(len);
+    if (expanded) {
+        if (prev_pos) {
+            snprintf(expanded, len, "%s%s", prev_pos, copy_pos);
+        } else {
+            snprintf(expanded, len, "%s", copy_pos);
+        }
+    }
+
+    /* caller free */
+    return expanded;
+}
+
 /* add_environment - add "key=value" to the current environment */
 int add_environment(const char *key, const char *val)
 {
     int n;
+    const char *expanded;
+
+    expanded = expand_environment(val);
+    if (!expanded) {
+        goto failed;
+    }
 
     for (n = 0; n < 31; n++) {
         if (!ENV[n]) {
-            size_t len = strlen(key) + strlen(val) + 2;
+            size_t len = strlen(key) + strlen(expanded) + 2;
             char *entry = malloc(len);
-            snprintf(entry, len, "%s=%s", key, val);
+            if (!entry) {
+                goto failed_cleanup;
+            }
+            snprintf(entry, len, "%s=%s", key, expanded);
+            free((char *)expanded);
             ENV[n] = entry;
             return 0;
+        } else {
+            char *entry;
+            size_t len = strlen(key);
+            if(!strncmp(ENV[n], key, len) && ENV[n][len] == '=') {
+                len = len + strlen(expanded) + 2;
+                entry = malloc(len);
+                if (!entry) {
+                    goto failed_cleanup;
+                }
+
+                free((char *)ENV[n]);
+                snprintf(entry, len, "%s=%s", key, expanded);
+                free((char *)expanded);
+                ENV[n] = entry;
+                return 0;
+            }
         }
     }
 
+failed_cleanup:
+    free((char *)expanded);
+failed:
+    ERROR("Fail to add env variable: %s. Not enough memory!", key);
     return 1;
 }