solver-c: harden parser/io and numerical output entrypoints

Improve stdin/file JSON ingestion safety and guard output paths against edge-case assumptions so solver binaries fail predictably instead of risking malformed reads.

Made-with: Cursor

solver-c/src/json_stdin.c

@@ -9,30 +9,49 @@
 #define JSON_MAX_SIZE (4 * 1024 * 1024)
 
 int solver_read_json_stdin(char **buffer_out, size_t *length_out) {
-    size_t cap = JSON_READ_CHUNK;
+    size_t cap = JSON_READ_CHUNK + 1;
     size_t len = 0;
     char *buf = (char *)malloc(cap);
     if (!buf) {
         return -1;
     }
     for (;;) {
-        size_t n = fread(buf + len, 1, JSON_READ_CHUNK, stdin);
+        size_t remaining = (cap > len) ? (cap - len - 1) : 0;
-        len += n;
+        if (remaining == 0) {
-        if (n < JSON_READ_CHUNK) {
+            if (cap > JSON_MAX_SIZE) {
-            break;
-        }
-        if (len + JSON_READ_CHUNK > JSON_MAX_SIZE) {
                 free(buf);
                 return -2;
             }
-        if (len + JSON_READ_CHUNK > cap) {
+            size_t next_cap = cap * 2;
-            cap *= 2;
+            if (next_cap > JSON_MAX_SIZE + 1) {
-            char *nb = (char *)realloc(buf, cap);
+                next_cap = JSON_MAX_SIZE + 1;
+            }
+            if (next_cap <= cap) {
+                free(buf);
+                return -2;
+            }
+            char *nb = (char *)realloc(buf, next_cap);
             if (!nb) {
                 free(buf);
                 return -3;
             }
             buf = nb;
+            cap = next_cap;
+            remaining = cap - len - 1;
+        }
+        size_t to_read = remaining < JSON_READ_CHUNK ? remaining : JSON_READ_CHUNK;
+        size_t n = fread(buf + len, 1, to_read, stdin);
+        len += n;
+        if (ferror(stdin)) {
+            free(buf);
+            return -4;
+        }
+        if (n < to_read) {
+            break;
+        }
+        if (len >= JSON_MAX_SIZE) {
+            free(buf);
+            return -2;
         }
     }
     buf[len] = '\0';

solver-c/src/main.c

@@ -4,6 +4,40 @@
 #include <stdlib.h>
 #include <string.h>
 
+static int read_json_file(const char *path, char **buf_out) {
+    FILE *fp = fopen(path, "rb");
+    if (!fp) {
+        return -1;
+    }
+    if (fseek(fp, 0, SEEK_END) != 0) {
+        fclose(fp);
+        return -2;
+    }
+    long sz = ftell(fp);
+    if (sz < 0) {
+        fclose(fp);
+        return -3;
+    }
+    if (fseek(fp, 0, SEEK_SET) != 0) {
+        fclose(fp);
+        return -4;
+    }
+    char *buf = (char *)malloc((size_t)sz + 1);
+    if (!buf) {
+        fclose(fp);
+        return -5;
+    }
+    size_t n = fread(buf, 1, (size_t)sz, fp);
+    fclose(fp);
+    if (n != (size_t)sz) {
+        free(buf);
+        return -6;
+    }
+    buf[sz] = '\0';
+    *buf_out = buf;
+    return 0;
+}
+
 static void print_json_output(const SolverInputs *inputs, const SolverOutputs *outputs) {
     printf("{\n");
     printf("  \"pointCount\": %d,\n", outputs->point_count);
@@ -33,8 +67,12 @@ static void print_json_output(const SolverInputs *inputs, const SolverOutputs *o
     }
     printf("  ],\n");
 
-    double pmin = outputs->pump_position_m[0];
+    double pmin = 0.0;
-    double pmax = outputs->pump_position_m[0];
+    double pmax = 0.0;
+    if (outputs->point_count > 0) {
+        pmin = outputs->pump_position_m[0];
+        pmax = outputs->pump_position_m[0];
+    }
     for (int i = 1; i < outputs->point_count; i++) {
         if (outputs->pump_position_m[i] < pmin) pmin = outputs->pump_position_m[i];
         if (outputs->pump_position_m[i] > pmax) pmax = outputs->pump_position_m[i];
@@ -143,18 +181,11 @@ int main(int argc, char **argv) {
         }
     } else if (argc == 2) {
         /* allow file path for tests */
-        FILE *fp = fopen(argv[1], "rb");
+        int rr = read_json_file(argv[1], &buf);
-        if (!fp) {
+        if (rr != 0) {
             fprintf(stderr, "usage: solver_main --stdin   OR   solver_main <path.json>\n");
             return 1;
         }
-        fseek(fp, 0, SEEK_END);
-        long sz = ftell(fp);
-        fseek(fp, 0, SEEK_SET);
-        buf = (char *)malloc((size_t)sz + 1);
-        fread(buf, 1, (size_t)sz, fp);
-        fclose(fp);
-        buf[sz] = '\0';
     } else {
         fprintf(stderr, "usage: solver_main --stdin   OR   solver_main <path.json>\n");
         return 1;

solver-c/src/main_fea.c

@@ -4,6 +4,40 @@
 #include <stdlib.h>
 #include <string.h>
 
+static int read_json_file(const char *path, char **buf_out) {
+    FILE *fp = fopen(path, "rb");
+    if (!fp) {
+        return -1;
+    }
+    if (fseek(fp, 0, SEEK_END) != 0) {
+        fclose(fp);
+        return -2;
+    }
+    long sz = ftell(fp);
+    if (sz < 0) {
+        fclose(fp);
+        return -3;
+    }
+    if (fseek(fp, 0, SEEK_SET) != 0) {
+        fclose(fp);
+        return -4;
+    }
+    char *buf = (char *)malloc((size_t)sz + 1);
+    if (!buf) {
+        fclose(fp);
+        return -5;
+    }
+    size_t n = fread(buf, 1, (size_t)sz, fp);
+    fclose(fp);
+    if (n != (size_t)sz) {
+        free(buf);
+        return -6;
+    }
+    buf[sz] = '\0';
+    *buf_out = buf;
+    return 0;
+}
+
 static void print_json_output(const SolverInputs *inputs, const SolverOutputs *outputs) {
     printf("{\n");
     printf("  \"pointCount\": %d,\n", outputs->point_count);
@@ -33,8 +67,12 @@ static void print_json_output(const SolverInputs *inputs, const SolverOutputs *o
     }
     printf("  ],\n");
 
-    double pmin = outputs->pump_position_m[0];
+    double pmin = 0.0;
-    double pmax = outputs->pump_position_m[0];
+    double pmax = 0.0;
+    if (outputs->point_count > 0) {
+        pmin = outputs->pump_position_m[0];
+        pmax = outputs->pump_position_m[0];
+    }
     for (int i = 1; i < outputs->point_count; i++) {
         if (outputs->pump_position_m[i] < pmin) pmin = outputs->pump_position_m[i];
         if (outputs->pump_position_m[i] > pmax) pmax = outputs->pump_position_m[i];
@@ -142,18 +180,11 @@ int main(int argc, char **argv) {
             return 1;
         }
     } else if (argc == 2) {
-        FILE *fp = fopen(argv[1], "rb");
+        int rr = read_json_file(argv[1], &buf);
-        if (!fp) {
+        if (rr != 0) {
             fprintf(stderr, "usage: solver_fea_main --stdin   OR   solver_fea_main <path.json>\n");
             return 1;
         }
-        fseek(fp, 0, SEEK_END);
-        long sz = ftell(fp);
-        fseek(fp, 0, SEEK_SET);
-        buf = (char *)malloc((size_t)sz + 1);
-        fread(buf, 1, (size_t)sz, fp);
-        fclose(fp);
-        buf[sz] = '\0';
     } else {
         fprintf(stderr, "usage: solver_fea_main --stdin   OR   solver_fea_main <path.json>\n");
         return 1;